Lol @ Sonic Generations being an easy plat. It is not. It takes a long time to get everything.
I think Jak and Daxter: TPL is the easiest plat (that I've earned) It literally does take a few hours. I would say Sly 1 but finishing a level takes a bit longer as well as the final boss than it does in J&D.
even if its ime consumng its still easy, like fallout 3 and AC2 time consuming games yet very easy to platinum
prince of Persia moveset: http://community.us.playstation.com/t5/PlayStation-All-Stars-Battle/Prince-of-Persia-in-all-stars/m-p/38273897#M125640
The Walking Dead! $20 for a full game that will literally make you **bleep** your pants in excitement and horror. And every single one of the trophies is story-based. This game gets Game of the Year 2012 for me, and I know that lots of others agree. Episode 5 comes out sometime in the next four weeks, but total this game takes (I'd say) around 10 to 15 hours to complete, so it's not a short PSN title. I guess it depends how much exploring and talking to NPCs you do though.
On another note, I personally find open-world games the easiest to Platinum. I have all the inFamous and Assassin's Creed games that I've played platinumed, and I plan on doing so with GTAV when that game comes out.
Edited for profanity.