Really? Why is that?

Halo came into the world as the only decent game on xbox with mainstream and casual appeal. Since it had literally zero competition it became a huge hit. Other devs saw the sales numbers but none of the reasons why it sold well and started to churn out mediocre fps after mediocre fps to the detriment of all other genres (and the fps market which is flooded with crap). Halo also brought with it the success of console online, and while devs focused solely on that, strong single player modes and local multiplayer, console gamings bread and butter, fell to the wayside in favor of slapping in some deathmatch and ctf modes.

A fine whine.

The FPS market is as big as it is because publishers have found a lot of success in making them. Less so those other genres which you believe have been crowded out by FPS games. Its not Halo's fault that the market changed the way it did, if anything it meant that something which would have happened anyway just happened sooner.

Certainly there are other factors, but the majority of the blame can be laid at the feet of MS, Halo, live and the marketing of them. It changed gaming, for the negative.

If Halo had never existed... we'd have less casual gamers.  What really helped the franchise was that it was aimed toward the masses which is what made it so successful. 

Just as you can place the blame for the abundance of open world games on Rockstar, the abundance of 2D/3D platformers on Nintendo and you can place the abundance of car racing games on Sony. Only really you can't because there isn't an abundance of these any more as all the copies turned into relative or absolute failures. Since we're now a generation beyond the first Halo game the abundance of FPS games can only really be blamed on the fact that they are really popular and are the most consistantly successful genre on the HD consoles at present.

I have more of an idea about the CoD franchise than you think.  For starters, UO was made by Gray Matter, not Treyarch (though it was later merged with Treyarch).   I was there from day one on the PC.  CoD was an amazing game but when the expansion came out, it grew by leaps and bounds.

UO had a lot more to do with the original than you think, it was an expansion after all.  It took the same engine and added things to it.  It was a step forward, while CoD 2 was a step back.  I never said that CoD2 had no vehicles because of Halo.  I meant that because of games like Halo, the face of PC FPS started to change and shift towards a more console desired specific (many being multiplat, console exclusive, poor PC support/patches and so on). 

And by "many people" you might mean the critics because I remember a lot of CoD and UO clans and communities didn't like the path that CoD2 was going down.  Like I said before, it was a big step back in terms of the direction they were taking.  The PC CoD community was not happy with CoD2.  And thus, CoD3 wasn't released on PC.  When CoD4 came out, it was finally what everyone was looking for in CoD2.  I firmly beleive that if CoD2 had kept the pace forward with UO, then we would have had a much better/higher selling game that would have paved the way for CoD3 on PC.

But then, aren't we agreeing on the same thing? No GTA3 no open world boom, no halo no crappy fps/ console online boom. And of course there's COD, which has been carrying on halos legacy of disaster.

I'd still play Ninja Gaiden Black and Bioware games, therefore I don't give a rat's ass about Halo being there or not, it was just another FPS I played. I've played a lot of FPS before it, and after it /shrug.

You really just don't have a clue do you?