The 2 star review is so wrong - the reviewer obviously did not check out first what he was actually buying.
The eTrex 30 is a very sophisticated piece of kit - incredibly quick to locate your position and very accurate (it can tell if you are on one side of a road or the other and the isosceles triangle icon on the screen not only shows your location but also the direction you are facing). The features and menu options are also very intuitive and the buttons and "toggle / joy-stick" are very easy to operate - you can do eveything with your thumb, even when wearing mits. The features such as the "trip meter" are brilliant (even tells you how long to sunset) and loading routes to and from your computer is a doddle.It has a three dimensional compass that very few GPS have - which means it works even when you are standing still (this is the only difference from the slightly cheaper eTrex 20). The altimeter is also very accurate. Phone apps are no-way comparable to what this piece of kit can do (also, using your phone as a GPS will run the battery down very quickly).
Two AA batteries do last the 25 hours advertised - Iam getting three days walking out of them.
I bought it so that I could download 1:2500 maps of specific areas as I need them. Two problems with this: 1) It works out very expensive (e,g. Lake District = £100) and 2) as the 2* reviewer says the "base map" on "BirdsEye" is so poor that you can not accurately identify the area that you you are purchasing - which means that you can make expensive mistakes. This is a pity as the "purchase only what you need" feature is supposed to be a big selling point - I have been told that my email complaining about this has been passed on to the boffins at Garmin.
Given the above, and the small screen size, I would advise purchasing the SD card of the 1:50,000 OS Map for the whole of the UK - this will add another £200 to the purchase price so you need to take this in to account when comparing with other products (although,if you see other reviews and comments for Etrex 20 and 30,there is advice on downloading maps for free).
The ETrex 30 is a sophisticated but easy piece of kit to use, it is nice and compact and durable for walking and running. However, if you need a larger screen (e.g. for the handlebars of a bike)I would go for the less sophisticated, older technology, but larger screened SatMap Active 10.(It is only because of the screen size that I do not give it 5 stars - but there has to be compromises!?)
Update (March 2014): It is now two years since I wrote the above review. My Etrex is still going strong and I still love it - and have relied on it in bad weather on a few occasions. The fact that the price is now down to £168 and the 1:50 map for whole of GB on micro SD card is now £137 (not withstanding comments that can get downloads for free)is , in my opinion, excellent value for money (I paid £230 for the Etrex when it first came out and remember the original - yellow - Etrex, which only provided a grid reference and a few "tracks" and no mapping capability, was around £120 over 15 years ago!