Uncharted.

It's just one, but to me it is the biggest one, just my opinion.

Demons souls/ dark souls / Valkyries chronicles/ stalker/ dawn of war/ Starcraft / disgaea/ blazblue

In short a whole lot

You missed out on Halo, which I consider the best game franchise around and I don't even play online. If you don't get an Xbox 360 at some point, you will miss out on what is sure to be the best game of the entire generation, Halo 4.

Play Vanquish.

Play it, and see the best that the HD systems have to offer.

If you get a 360, grab the Mass Effect trilogy. Solid.

TT, i dont even know where to begin lol

nothing really
just fancy hollywoodesque games
not even a proper DBZ game....a waste..

Yup, starcraft II, very hollywood-esque.

Uncharted, Assassins Creed and Dead Rising are my favorite new franchises this generation.

Oblivion

I was somewhat in the same situation, except I have a decent PC in addition to my Wii so I played the majority of third party games. However, I got a PS3 really cheap early this year only to discover that I really haven't missed that much. From what I played the following PS3 games are worth playing:
-Demons Souls and/or Dark Souls
-any Uncharted. I played 3, it's decent.
-Red Dead Redemption
and thats about it...I also played FF13, 13-2, God of War 3, Killzone 3, GTA 4 and Resistance 3 but none of those games are games that you miss out on if you don't play them.

Since you don't have a PC I would add Bioshock 1+2, Arkham City, Deus Ex: HR, Fallout: New Vegas and Portal 2 to the list.

I can not say anything about MS exclusives because I would rather stab myself to death with a wooden spoon than touch anything from them :P