The one thing I never got into with Halo series is the weapon selection. They always seemed off compared to other games weapons. I find the weapons to be sluggish, you'd think a sniper rifle shot wouldn't be able to be dodged after being fired, but it's entirely possible in Halo. Compare the sniper rifle in Halo 2 to the one in BF2142. No contest about the quality. I love the story, but the game play isn't exactly enough to make me want more and more.
And the first console FPS was probably Doom way back on SNES/Genesis. Unless Wolfenstein was on any consoles first. We've come a long way since then, with the addition of multiplayer and arena combat. Halo only became as popular due to xbox live and online play, which wasn't previously available to any FPS that I can think of. Halo 2 built off this fame, and 3 is even doing it again. Gears of war would be more popular if the 360 was the common household system but it's still not around as much as the xbox so of course it's not gonna get higher numbers than H2.
Graphically, Gears of War is orgasmic, and I expect even more of Halo 3. Their gameplay styles are pretty different, giving them equal draw to people with differing ideas of what's fun.
PC games will always provide more quality multiplayer modes than console games, as they're built for the online play more than they are built for the story modes. The only advantage to console games is they have an appliance with 100% dedicated gaming power, where PC's have other drains.
Oh and N64 Goldeneye/Perfect Dark = best console FPS engine ever.
