Disclaimer: I did not play Halo. In fact, I played very few FPS games after I got bored of Quake 3, and all of them were ANYTHING BUT simpler than it. They were slower, yes. Had worse controls, yes. Had dumbed down single player with retarded "story", yes. But, if anything, it made playing them more, not less complicated. It also made it less... wait, no, it simply made playing them no fun at all. OP's saying Halo is dumbed down and has worse controls, so I'm assuming it's exactly like those other games I played.
Maybe what you mean by "easy" is "less competitive"? It's not the matter of easiness or simplicity (it can't be, since Quake 3 is already the simplest and easiest an FPS game can be), it's the matter of artificially restraining the learning curve to make newbies able to play "experienced" players evenly. Well, I fail to see the fun in it. I fail to see the lasting appeal either.
What I assume you just had friends around to play Halo with. That's something most of the world doesn't have (XBox doesn't sell outside English-speaking world, period) and, as a consequence, Halo remains cemented in the XBox niche with the rest of the world basically not caring about it. Well, sure it's more fun to play a worse game than to not play at all. But all it demonstrates is that there were many people who bought a console and wanted to play on it. Well, I believe there's a Quake 3 version for 360 now, so I encourage you to get back to it (don't forget to introduce your friends to it, too). There's no need to play something inferior anymore.