Hmm, after some thinking through of my responses, I realize I haven't really answered the question you so like to ask right now. So I will, because I won't be satisfied if I don't.
I have already established that the PS3 is the platform with the best games for me (as far as I know by comparison at least). In general, I like deep and engaging singleplayer games, and I will rarely play multiplayer (unless local coop is an option. That I love. I would also never pay to get my console online unless there is a substantial point to it apart from online gaming). At the same time, I enjoy unique experiences, which is why I also want a Wii at some point and am looking forward to Sony's wands as well as Natal. On top of that, I am in general a fan of western games.
And as you might notice, I have a love for freedom of movement in games. You'll see in my games 
All of that comes together nicely in the PS3 for me. The funny thing is that I didn't know the PS3 would be the best for me when I bought it, I just took a stab at getting a console and got lucky.
With all the above in mind, here are the games I think makes the PS3 worthwhile for me, both released and yet to come, as well as exclusives and multiplats.
Uncharted series - The first game was really good, it had a very cinematic feel and a very engaging singleplayer, even though it had its faults. The 2nd game blew the first one away, as many of my gripes had been fixed, and the singleplayer had been made even deeper and more engaging! Uncharted: DF was my first platinum trophy, and Uncharted 2 was my third platinum trophy.
God of War III - Having played the two first games on the PS2, I have high hopes for this one. The two first games made themselves notable for me by having engaging singleplayer experiences with epic storylines. Especially the huge scale the games usually operate on, both in scenery and puzzles is something I am really looking forward to seeing on the PS3.
Heavy Rain - The epiphany of interactive game telling? Maybe. I know this is most likely one of the most important games of the generation, no matter how good it will be.
Mirror's Edge - The game falls flat in its storytelling and in many ways, also in its presentation. But the main mechanic, the running, is quite deep with the right leveldesign, which is something the game accomplishes nicely most of the time, resulting in a game that feels incredible (once you get the hang of the running. Getting the hang of it can be frustrating at times). This is most notable in time laps, and I would take a Mirror's Edge time lap racer over an ordinary racer any day. Mirror's Edge was my second platinum trophy.
Batman: Arkham Asylum - A culmination of almost all things great about videogames and the worlds greatest detective. A deep and engaging storyline, and the first game to really let you become the Batman. An amazing game all in all, despite some annoying challenge rooms, stopping me from getting the platinum trophy 
Assassin's Creed series - The first game was a little lacking. Good ideas, flawed execution, but still a good game. The second game looks to rectify most of the flaws in the first one, making for an even more engaging experience than the first one. One of the things I also really liked about the first one was the freedom of movement (bringing me back to Mirror's Edge for instance).
inFAMOUS - A fun sandbox game, much better done than Assassin's Creed in terms of the world. The freedom of movement is incredible, I really love it, and on top of that, it has great combat and a good and well-executed storyline. Great game.
Metal Gear Solid 4: Guns of the Patriots - Best... story... ever... Honestly, this is still my favorite PS3 game, probably my all time favorite game (though I hesitate to give that title to any game). I didn't even play the other MGS games before, I just watched a recap of the story on GT. Extremely engaging singleplayer, though Uncharted 2 leaves it in the dust storytelling wise.
Flower - Amazing, breathtaking experience. Truly poetry on gameform, it really is something in a category of its own, I absolutely adore this game. Extremely engaging singleplayer experience.
I could go on
