The one game for me that makes PS3 the console to buy is LittleBigPLanet.

The reason isn't because it's my favourite game; that belongs to Valkyria Chronicles, so far.

The reason is because it is the game EVERYONE who comes here and plays on my PS3 loves and wants to play. Adults and kids fall in love with the game the minute they see it. It brings such joy to those playing it and watching it being played. I like playing it with my kids (it's the only time I like playing it really), my kids like playing it with each other, my kids friends only want to play LBP when they come here (OK I don't have too many Coop games, but I still think LBP would be the one they want to play most). Even kids who don't play console games love it.

But on top of the fact that everyone loves it the game itself is so great. The gameplay is great, the style is great, the graphics are great, the online is great, the play create share is great. I am looking forward to Mod Nation Racer, but I don't think it will top LBP.

Arguably it's the game of the generation.

If there is only one PS3 game that deserves to sell more than 10 million, it's this game.

So, what's the one game that made the consoles you own a no brainer decision?

PS You'll note I have the DS in my profile. The reason I haven't written about the DS is because it's not actually mine. There are 2 DS's in the house and they are both owned by my sons. I've only watched them play, and not very often. So there isn't a game on DS I know of that compels me to have one.

I consistently upgrade my PC when a new Blizzard game comes along. I upgraded it for Starcraft, again for Diablo 2, again for Warcraft 3 (twice), again World of Warcraft, and again for the upcoming Starcraft 2 (made an early upgrade coz I couldn't take it anymore).

P.S. I know it's not a console, but Blizzard games make me want to buy hardware. 

Nice let me be the first to say uncharted 2 makes the ps3 a must own.

I'm not prejudiced here. If people want to talk about the game(s) that make them need to max out their PC specs then that is a legitimate contribution to this thread. Games aren't the reason I need to own a PC and they certainly don't make me want to fork out cash on a regular basis to keep my PC up with the minimum specs for the latest PC games. But people who are that way inclined deserve to be heard.

@ lilc64: And for your 360...? This isn't a PS3 love fest.

Mario galaxy was the no brainer that made me get a Wii, when i saw it i had to have it. so i bought the Wii for it, but NSMBWii would have had the same effect on me :)

Super Mario Galaxy on the Wii pure magic

Metal Gear Solid is the reason why the PS3 is a must buy in my opinion, although it only applies to fans that have been with the series ever since the beginning. I played MGS4 with a group of friends, we handed off the controller, and it was a magical experience. We all cheered at the beginning of Act 4.

If you're not an MGS fan, then I'd say Uncharted 2 is the reason to own a PS3. U2 is to the PS3 as Raiders of the Lost Ark was to movie theaters in 1981. :p

I know the thread is young, but c'mon, who can forget Halo 3 for the 360? This is one of the best party games ever, plus the co-op campaign is awesome.

For me, the games that made me buy my consoles and handhelds are as follows:

360: Call of Duty 2
PS3: Final Fantasy XIII (bought at launch)
Wii: Wii Sports and Wario Ware
DS: Professor Layton
PSP: Crisis Core (bought at launch)

Tons of "must buy" games for each console, now. The first "must buy" for each, in my opinion was:

DS: Mario 64 DS (2005)
360: Gears of War (2006)
Wii: Twilight Princess (2006)
PS3: MGS4: Guns of the Patriots (2007) -incidentally, a month ago, my kid was studying Paul Revere. The terms "Sons of Liberty", "Patriots", and "Guns of the Patriots" were all mentioned in her textbook. My mind was blown!
PSP: Final Fantasy Tactics