Do you want me to get a list out...

If you are talking about sales then Wii Fit is a Halo Killer. If you are talking about quality Halo got killed long before Killzone 2 even came out.

Halo was setting all kinds of multiplayer benchmarks. Killzone, well it's setting graphical benchmarks for the PS3 (and 360). I'd be surprised if it's as popular as Halo 3 in the multiplayer stakes and whether it will receive the level of multi player support Halo 3 got over the years. It's down to PS3 fans I guess. (Wonders how popular Resistence 2 is multiplayer wise...).

KZ2 is by no means a Halo killer. The storyline and graphics are cool, but it's just not anywhere near as fun. The controls are a bit aggrivating (because the PS3 controller wasn't created with FPS in mind), but it's still a good game. I've played various games that play like KZ2. It's by no means unique like Halo, nor does it have replay value on par with Halo.

Sony doesn't make games, they publish them.

We are talking about shooters and more specifically 1st person shooters. Why bring Wii fit in the discussion? To me a killer software is one that takes sales/popularity from an existing title and transfers it to another (ie, if Halo players stoped playing halo to play Wii fit, thus wii fit taking sales/popularity away from halo, then Wii fit is killing the halo franchise, but of course we know this is not the case). If anything halo has killed so many other franchises, and continues to do so, as so many shooters come and go, but halo remains (people play the new title/shooter, the fad fades, then they go back to playing halo, and rarely go back to play the new title). This is why it remains a top 2 most played game on Live, >18 months after release. CoD4 - 5 is the only franchise to come close to Halo as there is a loyal/growing following, and if anything CoD6 (CoD:MC2, on the PS3 itself) is more likely to 'kill' KZ2 than anything else.

Why does everyone dis Halo's quality? It's not often that an FPS has splitscreen, co-op, and online splitscreen.

While KZ2 is fun, it lacks variety. Like S.T.A.G.E. said, the replay value isn't as good as Halo's. The graphics are nothing - graphics arn't what make a game.

If we are going to compare apples to oranges, then the Balance Board is very close to being a PS3 Killer. 

From a person who owned both games, Halo is alot more fun and addicting.

Split Screen and Multiplayer story mode.