PS3 games for the uncoordinated gamer?

Oblivion! Has an easy mode, astonishingly big world, and you can compensate for poor coordination by getting hugely skilled in alchemy and marksmanship and simply one-shot killing everything before it has a chance to attack you. Plus you'll be all prepared for when the next game, Skyrim, comes out in November. Be warned: this is a MASSIVE open-world RPG and it is easily possible that you will spend 300+ hours playing it.

I hit the same problem with Portal 2 as I did with Portal: final boss, done. Not going to be able to finish it without a huge investment of time in this one five-minute bit. Too much other stuff to do. That said, it is an amazing experience, and I'm absolutely glad I bought it. I do wish there was a "I know I'm completely naff at this, can you show me how it ends?" option on games sometimes. It's like being forced to walk out right at the climax of a movie.

Seconding Fallout 3 and Fallout: New Vegas. I am excellent at annoying tricky jump games (hi, Mirror's Edge), and I play Fallout 3 when I just want to chill and not toss the controller across the room in frustration. V.A.T.S. makes combat much easier, especially if you ramp up your attack skills early and take any V.A.T.S.-centric perks (Action Boy, Grim Reaper's Sprint, etc.). Like Oblivion, once you reach a certain level, you can generally kill enemies in one hit.

Might and Magic: Clash of Heroes! It's a wonderful little puzzle game with RPG elements. Totally turn-based, no coordination required. NB: It's a downloadable game from the PS Store, so get a PS Store card from Gamestop rather than giving them your CC info.

Also, are you interested in Japanese role-playing games at all? JRPGs come in all shapes and sizes, but they're often turn-based and forgiving of failure. Strangely, the PS3 isn't a great platform for JRPGs, but http://www.amazon.com/PS3-JRPGs/lm/R3BN815HP8RUYB of the good ones (including some outliers like Nier). Eternal Sonata in particular has a striking visual style. If your PS3 has PS2 backwards compatibility, there's a whole world of amazing JRPGs at your fingertips. In particular I recommend http://en.wikipedia.org/wiki/Shin_Megami_Tensei:_Persona_3 and http://en.wikipedia.org/wiki/Shin_Megami_Tensei:_Persona_4.

I haven't played Portal 2, but be warned that, while Portal is absolutely amazing, it seriously and unexpectedly ramps up the fine-motor-control difficulty (as opposed to puzzle solving difficulty) in the final five minutes of the game. After more than an hour of frustration knowing what I needed to do, but being unable to coerce my avatar into doing it, I had to call on a friend who, being a more avid gamer, was able to complete it with ease on the first try.

FWIW, I found Mass Effect too twitchy and difficult to be fun for me to play. It has timed missions and stuff.

Portal and Portal 2. Red Dead Redemption is pretty easy, as any gunfighting involves locking on first. I am just like you and had no problem with it. Plus it's a sensational, brilliant, stunning game, best I've played ever really. L.A. Noire -- quite atmospheric, and even though it has action sequences, if you fail at them three times in a row, it lets you skip them. Plus it's a huge world. Bioshock has combat and stuff, but I am just like you and had no real problem advancing in easy mode. That one is stunning too.

If you're into older games, you could look at Final Fantasy Tactics on the PSN. Or the other FFs like 7, 8, or 9, though some of the mini-games might be troublesome. Another possibility might be the Dungeon Hunter game on PSN. It's an RPG, too.