The funny thing is, Halo did a fair number of things right. The outdoor environments were spacious and interesting, the vehicles were a hoot to drive around in (once you got used to the unintuitive but sensible control scheme for them), the voice acting was pretty good, and some of the action sequences were fun. It didn't "ruin" FPS games, just brought a somewhat distilled version of them to the 6th-generation consoles.
The trouble with Halo is the guilt-by-association problem that it has with a large number of its fanboys (please note I say "fanboys" here and not "fans"), and that too many companies took what Halo did wrong as examples of what they should do. It's unfair to lay these things at Bungie's feet (while their lackluster sequels can be, quite fairly).
If you want to blame someone for the plethora of games that tried to copy Halo- and those games' success over higher-quality ones- look no further than the gamers themselves. It's their dollars that dictate what succeeds and what fails.
