Congratz on getting a ps3. I'm sure you'll enjoy it.

As far as games go, LBP, Demon's Souls, and Uncharted 2 are the highlights for me, in that order.

To learn more about Demon's Souls, I'd suggest reading this write up by Gamasutra. It's easily the best piece I've seen on the game, and it describes why I couldn't put the game down to a T.

Edit:

Ok, I'll give my thoughts on Demon's Souls.

The game's design is really more Zelda-esque than anything RPG-ish, notably the level design.  The level design is not simply a bunch of similar dungeons made up of repeating and randomly placed tunnels and whatnot.  It is wholely unlike Final Fantasy, Dragon Quest, and Oblivion in this regard.  Instead, each dungeon has a very unique style, with every place being distinct from every other.  Much like the dungeons in Zelda, you can always tell exactly where you are when playing Demon's Souls.  This not only makes it easier to find your way around, but it makes for a much more memorable experience than most RPGs.

On top of that, the combat is more hack n' slash than RPG, but rather than flashy Ninja Gaiden-esque combos, they give you a few simple attacks, and it's all about using the thrusts and parries effectively to combat your enemies. In all honesty, getting to know your enemy is probably more important than the items you're carrying (though they're an integral part of the equation too).

However, the game is most definitely an RPG, given that you do gain experience, and given that you have a plethora of weapons, armor, spells, and other items that you can find, buy, and craft, thus giving you great control over what type of being your character becomes.

My favorite part of the game is how it handles death.  In this game, there are no game over screens or anything of the sort.  When you die, you don't have to start anything over.  Instead, when you do die you are stripped of your body, and forced to roam around the land as a phantom.  You do go back to the beginning of the immediate level you were playing, but any items you found prior to death remain on you, any events you triggered remain triggered, and the only thing you've lost are any souls you had on you at the time you died (souls are used for currency and for increasing your stats).  Yet even then, any souls you had can be found on the bloodstain residing at the location of your death.  Make it to your bloodstain intact, and you get all those souls back!  But be wary, as if you are slain again, a NEW bloodstain is created at the new point of death, so everything at your previous bloodstain is lost.   Considering you'll likely have to fight your way back to your bloodstain, you'll probably gain quite a few souls on the trip there, thus essentially doubling your total souls if you do manage to get to your bloodstain.  It's a gamble you may or may not wish to take, but it can be well worth it.

The reason I am fond of this system is that even in death, the game feels like it's still progressing.  You feel like you're getting somewhere, even if you died.

I highly recommend the title.  It's the most unique RPG I've yet had the pleasure of playing, and it's my favorite third person adventure game behind the 3D Zeldas.  It's right up there with LBP as my favorite ps3 game, and easily in my top ten games of all time.  It's probably 6th, actually, right behind the 3D Zeldas and LBP.