On PS3 only games I own are those listed above in my first post
On the 360 I have:
Gears of War/2
Halo Reach
Left 4 Dead 2
Batman Arkham Asylum
Modern Warfare 2
Assasins Creed II/Brotherhood
Need for Speed Shift/Hot Pursuit/Shift 2
FIFA 10/WORLD CUP SOUTH AFRICA/11
The Force Unleashed/2
WWE SvR 2011
NBA 2K11
F1 2010
GTA IV
Red Dead Redemption
Bad Company 2
Black Ops
Brink
DiRT 3
Dead Space 2
Crysis 2
Bulletstorm
Portal 2
Mortal Kombat
LA NOIRE
Dante's Inferno
Forza Motorsport 3
EA MMA
Shawn White Skate
Marvel vs Capcom 3
Super Street Fighter IV
Mass Effect/2
Spiderman:Shattered Dimensions
Medal of Honor
WWE All Stars
So I think I have played all good multi plaform games that why I am looking into exclusives.
I am not into those japanese type games like Disgea,Valkirya Chronicles,Yakuza and Folkore,but I will buy Rathet and Clank for sure

Yeah if you plan on getting the MGS HD collection then I would hold off on MGS4 until you finish those first and I'd look into playing MGS1 aswel if your interested in following the whole series story. A knowledge or the series improves your experiance drasticly.

Other than that I suggest you get Demon Souls or Resistance 1 and 2,

Metal Gear Solid 4, Valkyria Chronicles & Uncharted 2...you dont need more ^^

You can download MGS1 off the PS Store.

You need to play MGS4 last, I beg you to play them, they are stunning games.

I recommend you play MGS1-3, then Peace Walker, then MGS4.