=== Update after a year's ownership ===
I still love my G2 but I tend not to use it much. I found that the improvements of the FZ150 over the FZ100 solved the picture quality issues of the FZ100, so there is less need for the G2 when I want a sharp picture. I've also subsequently bought a Nikon D5100 as an upgrade from my D50 (following some substantial price reductions) for macro work. The D5100 comfortably out-performs the G2 in terms of resolution and low-light performance, so the G2 now falls into a kind of no-man's land in my kit. That said, I'm keeping my G2 as it allows me to use my old lenses where my Nikon SLR doesn't, but I can't actually recall when I last used my G2. The bottom line is, If I could only have one camera, it would be my FZ150.
=== The background ===
The whole idea of a bridge camera is a camera that gives advanced exposure control and produces high quality results, in a package that is more compact and convenient than an SLR. However, until the Four Thirds sensor cameras were released by Panasonic and Olympus, the "bridge" camera was essentially a greatly accessorised compact camera. With a fixed lens, the only option to give the user as much flexibility as possible was to provide a zoom lens with ever increasing focal range. To keep the size of this "superzoom" lens acceptable to a wide number of users, the sensor was kept small: The bigger the sensor, the bigger the lens needed to fill it to the edge.
Whilst this approach gave rise to some remarkable cameras, none were really comparable to the quality offered by an SLR. Often, even fairly modest cropping, far less "pixel-peeping", reveals both a lack of fine detail (a smearing effect) and a surplus of noise (speckles of random colour) in pictures taken under ideal conditions. Problems that only get worse in poor light when more is asked of the little sensor. The FZ100 sensor squeezes 14MP onto a 6.12 x 4.51mm sensor, whereas the G2 has 12MP stretching their legs on a 17.3 x 13mm sensor. With each pixel being considerably larger, more light can reach each pixel and noise levels are reduced considerably. This means pictures can be cropped closer without losing visible quality.
As the delighted owner of a Panasonic FZ100, like the husband of a fading beauty, I dearly loved my photographic partner but sometimes longed for one that was a little more appealing when viewed close-up. I have an SLR, but I find it a little too big to carry around as often as I want a camera. More importantly to me, SLRs don't "do" live-view or video particularly well.
The micro four thirds (m43) standard lives in the shadow of "better" SLR cameras, and yet is more expensive than most fixed lens bridge cameras with a "superzoom" lens. And that's only the start, do NOT underestimate the cost of additional lenses. Even "cheap" lenses designed for m43 (micro four-thirds) cameras cost around £200. Fortunately, the m43 has a trick up its' sleeve that cuts costs somewhat. You can buy adaptors that will allow you to fit almost ANY SLR lens to an m43 camera. This means that the lovely selection of lenses you have from your old SLR (in my case a Minolta X700) can be fitted to your m43. (There is a 2x multiplying factor, so your old 50mm is a 100mm lens on m43.) How cool is that? Additionally, there is an active and growing m43 user community who are very helpful, particularly for film-makers.
=== The overview ===
Anyway, about the DMC-G2. To anyone familiar with the FZ100, there is a great sense of déjà vu about the G2. With battery, card and cap, the FZ100 weighs 552g whilst the G2 with stock 14-42mm lens weighs 601g: A difference of about the weight of four AAA alkaline batteries.
The back panel is, at first glance, identical. However there are some changes in the button functions, and more importantly, a considerably larger Electronic ViewFinder. This EVF is quite a revelation. I have, on rare occasions, used the FZ100 EVF and am on record as describing it as a somewhat pointless and nasty little peep-hole. I'm surprised and delighted to find that the G2 EVF is excellent, and vastly superior to the viewfinder FZ100 and even to that on my Nikon DX-format SLR. The EVF is actually provides much the same sized view as a full-frame SLR viewfinder. Don't dismiss the viewfinder as a factor when choosing a camera. If you're upgrading from a compact to an interchangable-lens system, you might find the APS-C or DX SLR format viewfinder uncomfortably small with extended use, particularly if you wear spectacles. Compare a DX and FX SLR and you'll see what I mean.
At the front, in place of the FZ100's silky-smooth 25-600mm (equivalent) zoom, is a slightly slower 28-84mm (equivalent) zoom. It took a little use to become comfortable with the feel of the manual zoom, but it feels natural now. In fact the electric zoom doesn't feel right now, so I suppose it's what you get used to. Anyway, the auto-focus of the G2 appears to be on a par with the FZ100. Low light/low contrast subjects can still defeat it, but it works quickly and quietly in less challenging conditions. The neat manual/close-up/normal focus switch on the barrel of the FZ100 lens has moved to a switch round a dial on the top panel to the left of the EVF. However, with this move is another subtle rearrangement of functions. Now the three position switch selects from manual/normal/continuous focus, whilst the dial itself is the auto-focus mode: Face detection/tracking/23 area/single area. I like this new arrangement. Additionally, the touch-screen provides a terrific touch-to-focus feature. This allows the user to touch a point on the screen to set the focus point. The thumb-wheel then allows you to set the size of the focus area, which is useful.
The old "close-up" switch has evolved to a mode in itself on the main top dial, with four sub-settings to choose from: Flower/Food/Object/Creative. "Creative" being some kind of D.O.F. control. I'm tempted to be slightly scornful of these new modes, but I'll see how well they work. Panasonic modes tend to be a lot cleverer that they are given credit for.
Actually, given that the Panasonic scene modes have previously been so good, it was disappointing that when I went looking for them and set the dial to "SCN", instead of the plethora of options offered by the FZ100, I found six. Sunset, Party, Baby1, Baby2, Pet and "Peripheral Defocus". I'm looking forward to experimenting with "Peripheral Defocus" but having learned to trust the Panasonic scene modes in my Panasonic TZ5 and FZ100, it's quite a loss to see them axed for the G2. Maybe there's a load of them tucked away in a sub-menu somewhere. I live in hope and will update this review if I find them or confirm they really aren't there, I'm still working my way through the manual. Incidentally, I've seen some reviewers bleating about the manual: The G2 is a complicated camera and requires a lot of explaining. Panasonic manuals start at the beginning, and slowly and logically works their way through all the camera's features. The G2 manual is no different. It's not a novel, and it's not a quick-start guide. G2 owners will have to do some reading and learning: Deal with it!
=== In Use ===
Using the kit lens produces excellent results. There is a slight tendency to over-expose (to my mind) but that's easily compensated for and there are comprehensive bracketing options of 3, 5 & 7 frames in steps down to 1/3 stop.
As much of my photography is macro, it's quite a luxury to pop a close-up lens onto the kit lens and have the benefit of auto-focus. The pleasure of being able to touch the point I wish to focus on, and have the camera snap onto it is almost visceral. Brilliant! Swapping the kit lens for my old Minolta 35mm f1.8 lens, with a suitable adaptor on the back and a +10 close-up lens on the front, I have an excellent budget macro set-up that has allowed me to take some great pictures. A press of the thumbwheel is my preferred way to toggle the focus-zoom, but it's not the only way. A remote shutter release plugged into the 2.5mm accessory socket ensures a steady shot without the benefit of OIS. Manual focus is also available with the kit lens, of which the focus ring is nicely geared and achieving very accurate focussing is easy. In fact so far I've been so pleased by the ease of manual focussing, I haven't actually used the close-up modes at all.
Further use of the camera reveals that some of the switchgear is context sensitive. It's all fairly logical and quickly becomes second-nature, but it is a little bewildering at first. The G2 is a well-made camera that operates with a reassuringly expensive sounding mechanical click upon the shutter release.
As with the FZ100, familiarity breeds affection, and the more I use the G2, the more I enjoy using it. I now find the G2 to be increasingly intuitive to use, greatly facilitated by the touch-screen. Make no mistake: The touch-screen is here to stay! But for traditionalists, I love how the G2 alows more than one way to access a function on the camera, letting the user choose their preferred method. You're not forced to use the touch-screen, but it's silly not to if you can. A capacitive touch-screen might be nicer, but possibly at the cost of accuracy. I'd say the only fault with the screen is that it's not a 920,000 pixel one.
I really appreciate the "film", ISO and white balance buttons on the rear D-pad. Very handy! You can also program a button for a function of your choice, which I find neat, but at the time of writing I can't actually remember what I programmed mine to do! :) The touch and slide exposure compensation on the rear-screen is pretty cool and drew an impressed "Ooh!" from my companion, but in practice I found it a little fiddly to use. However the traditional controls are to hand if you're wearing gloves or have big sausage fingers. I've actually found that putting the camera in manual and setting the aperture and shutter manually according to the exposure meter on the display works most conveniently for me.
I really like the way I can choose the way I shoot with the G2, I'm not forced to do things a particular way. All touch-screen, all buttons or a mix of both. Have it your way, to coin a phrase.
=== Downsides ===
The G2 and the FZ100 are only superficially similar cameras, in use they suit different styles of photography. The G2 doesn't have the va-va-voom of the FZ100: There's no big, fast zoom. So I have to move myself around more. There's no 11fps burst mode, so I have to be more skillful in my photography. I miss the 11fps a lot on the G2, it's a great feature.
=== In conclusion ===
Like the FZ100, the G2 is much greater than the sum of it's parts. Panasonic seem to have a knack for making cameras that are both a real pleasure to use, and don't stop you doing something you want to try due to a lack of functionality. I intended to upgrade from my FZ100 to the G2, but the FZ100 is so good at what it does, that I may well keep it AND my G2. Especially as all the accessories (bar the conversion lens adaptor) work equally well on either FZ100 or G2. The FZ100 is an excellent camera to take with you when you go out and about. The G2 is an excellent camera to take when you go out specifically to take photographs. If I could only have one, it'd be the G2. But I'd miss my FZ100.
P.S I sold my FZ100, found I really DID miss it, and replaced it with an FZ150. Bliss, at a price! ;-)