Final Fantasy XIII looks brilliant, and the characters have some interesting traits, but overall the story is lacklustre and so disjointed (as it makes use of a 'Day xx' chapter break, much like KH2, but unfortunately I don't think they have pulled it off nearly as well as the KH2 implementation.)
As for RPGs - It really depends on your preference. RPG, JRPG, SRPG etc.
Valkyria Chronicles is a superb game, with a great plot and a unique visual presentation (just knowing it uses the 'Canvas Engine' should give you a hint as to the visual style)
Disgaea 3 is fun and has decent English VA, but it is heavy on grinding (much like the previous games in the series), but the main character, Mao, doesn't compare to Laharl (or even Adell for that matter) from the previous games.
Demon Souls is another title worth a look at, although it certainly isn't for everyone. If you want to play with a DMC mindset (mashing the attack buttons and jumping everywhere) then steer clear of this game and pick up DMC4 or Bayonetta (which I personally feel has a better battle-system implementation than DMC!)
Cross Edge is an interesting game - It's basically a cross-over title, with an average story, but some very memorable moments (mainly comical ones). Like Disgaea, it's a grinding game, but if you are happy at leaving missing trophies, then it's not too hard to complete in a few sittings.
As for PSN downloads - Vagrant Story (PSX) is available; which I would highly recommend if you haven't played it before and are not too bothered by the graphics (although they were beyond their time when it was originally released.)
BoF3 is there too - I personally preferred 4, but this was still a good game in it's own right.
All of the PSX FF's are there too, so if you have a liking for 7,8 or 9 and haven't played or no longer have the discs, then maybe download these too.
For Non-RPG games, I'd recommend:
Bayonetta (if you can get past the shameless fan-service), Fallout 3 GOTY (still has a large RPG element, but has it's fair share of action - Overall an engrossing game, but maybe a little slow for some people), Metal Gear Solid (superb single-player and the online game is refreshing different to games like CoD; but the community isn't the best around), Resident Evil 5 (now that it's released, it's best to go for the Gold version with all the DLC included.) :exhausted:
I could go on listing titles, but I'm sure you have better things than reading an even longer post.