Modern Warfare probably didn't deserve to be that high (definitely within the top 10 though).
Metroid Prime is not really a FPS (but you do shoot things a lot in first person).
Halo would have been a 6-10 game for me. People (that is, PS3 fanboys) don't seem to understand that it was Halo that paved the way for Killzone, Resistance and all your other favourite console FPS's to be successful, it pretty much established a benchmark. Not many games can make a claim to that, certainly the top 5 have.
I don't really get why Killzone 2 would deserve to be on this list, it really didn't do anything to stand out at the top of the FPS pile or anything really original (except accelerating turning). It's not a bad game at all (it's pretty great once you get used to the controls), it's just not top 20 greatest FPS (of course, that's imo).
System Shock 2 probably deserved to be on the list more than Bioshock did (though I enjoyed Bioshock way more)
Overall, it's not a bad list and there's no choices to cringe at (which is good).
I won't even mention Resistance......











