Mass Effect on PS3...I never thought we'd see the day, but here we are. While I still dream that the first ME game would cross over to Sony's platform, the arrival of ME2 and the news ME3 will be on PS3 too makes up for it (as does a PS3 exclusive interactive short comic that helps you not only get to speed on the back story of the first game, but lets you make decisions to help shape your ME2 experience). You see, the beauty of ME is that your game plays out uniquely to you - if a character dies it ME1 he or she won't be there in ME2 and so forth (so for the uninitiated, keep your ME2 game saves!). It's not the same as playing the original (and if you get a chance to I fully recommend it), but it the interactive comic (created by Dark Horse no less) is the next best thing.
If you've played the original on the 360, you'll know what Mass Effect will offer you. If you haven't played Mass Effect, essentially the game is part shooter, part RPG, with plenty of ways of creating 'your' story around the main linear storyline - everything from Shepard's gender, how he/she looks (the character create is amazing) to how he/she chooses to talk to other characters (passive, aggressive, or not at all) is up to you. You can also choose your powers (you can be a soldier who relies on shooting to get them through, or vanguards or engineers, which enables you to have special biotic powers for example. The game is dialogue heavy, so if you're someone who skips cut scenes to get straight to the action, you're probably best off elsewhere. However, Bioware are masters at this kind of thing and ME2 excells in almost every way over its already incredible predecessor. A nice touch in ME2s dialogue is the introduction of paragon and renegade actions - at certain points in the game, you will have the chance (via an on-screen indication) whether to choose to do a paragon action (for example, intervening if a teammate is about to shoot someone) or a renagade action (at one point I was talking to a particularly uncooperative alien who ended up being chucked out of a window courtesy of my renegade action). The joy in this is you can of course ignore the suggestion, so if you think that bad guy your teammate is about to shoot right through the head really does deserve to meet his maker, you can stand and do nothing.
A difference beween ME and ME2 is that ME2 definately leans towards a shooter rather than an RPG - levelling up (to a max of level 30) and upgrading your character is much easier and automatic if you choose it to be. So while the RPG elements are perhaps a little watered down, the combat has been scaled up - cover simplified (for example being able to sprint to cover with the same button press) and the range of tactics that can be brought to the table to defeat enemies is exhaustive (including instructing what powers your team mates should use in battle on the fly). You also select what members of your team will be best at a particular mission, for example if you know that a certain type of enemy (let's say an enemy who have strong armour) will be involved in one mission you can choose a team member with the 'incinerate' skill to burn through armour quickly. So, if you have played ME on XBOX, it does move into more action territory, but that's not to say there's not a depth to the combat or the RPG elements of ME2.
Another possible negative that I have seen discussed is that the size of the team is too large for you to feel connection to the characters. This is understandable (it is a big team), however I feel with the game structure being as it is, Bioware have taken steps to ensure that all team members get a run out with you. Without giving too much away (because I hate it when reviews do that), you have a main mission that you have to recruit a team for (I won't reveal specific mission details as again, I wish to spoil nothing). Each teammate you recruit then has a side mission for you to complete with them, thus meaning you spend time with them. One reason why this works is the strength of the characters - in most games like this, people will have their favourites, however picking your final squads is tricky in ME2, each character brings something special to the team and each character affects how the game pans out in subtle ways. Each member has their own strong back story and different reasons for you to relate to them. Another point to note with this mission structure is how it helps you mix side missions with main missions. For example, in the original ME, I did all the side missions first, then went to the main missions. In ME2 it feels like the side missions are linked to what you're doing at the time, making the experience seemless (for example, there are times where you have a primary mission to do, but a side mission will take place in the sane area, meaning that you will see to the side project also, rather than just skipping it.
Another difference introduced in ME2 is planetary exploration - now you use a scanner to go over planets in search for minerals that can be used towards research projects (like weapon and armour upgrades). It's still not perfect, but it's more interesting than in ME where you would just click on a planet and get a bit of text explaining what happens there.
I've read a couple of reviews that have said the ending is underwhelming. I'm honestly confused by this, the build up to the final mission is intense and you even get a boss fight that doesn't feel like a run-of-the-mill end-of-game tacked-on boss fight (I'm looking at you Bioshock!) The final mission is dramatic, whilst leaving it open for what may come in the third installment.
As for PS3 to XBOX differences, you have the interactive comic as I've mentioned, and you also get a whole bundle of DLC thrown in (perhaps to ease the pain of not having had ME on Playstation before!) The DLC has had mixed reviews when released on XBOX (especially the Kasumi DLC). However, as PS3 owners get it from the off, it doesn't seem out of place or that it's an expensive add on. The Lair of the Shadow Broker is especially good. Looks wise I think the PS3 shades it, but whichever console you're on, ME2 is a good looking game, notably the characters themselves.
Overall, if you liked Mass Effect, you'll love ME2. The Mass Effect series is an experience that any gamer should try, it's less a game and more a sci-fi epic that you control. In my review for InFamous on PS3, I said it was the kind of game that you thought about even when you weren't playing it. ME2 goes one better, it's the kind of gaming experience that stays with you after you've completed it, and as it clocks in at over 30 hours, it's incredible how Bioware have created a game that you immediately want to go back to, to see in what other ways the game could play out (on a side note, if you try and do every single mission and scan every planet to find every secret mission, you're looking at a good 42 hours or so!) Graphically, the game is excellent, the dialogue is top notch (as is the music score), the missions are varied and always interesting and replayability is strong (because you're going to want to do it all over again and be a total renegade!). There's no two ways about it, Mass Effect 2 is an essential purchase whether you've played the original (or, as I have, ME2 on XBOX as well). Now it's arrived on PS3, the best series of this console generation is available on two excellent gaming platforms and that can only be a good thing.
***QUICK EDIT - there's been a lot of talk of the save game bug affecting some Mass Effect 2 players (for more details google Mass Effect 2 ps3 bug). I played through the game with no problems whatsoever and am currently playing through again, also a friend of mine has completed it with no trouble whatsoever. That's not to say it doesn't exist though, as there have been many reports of consoles freezing and corrupting the save data. A patch is apparently in the works to fix this problem - as I said though, my playthrough was absolutely fine (and the word from Bioware is that if you reset your console after every mission it helps any save issues).