I think Halo was a hit only because Console guys had never played any Quake type game before it. PC guys look at it and see a game they played five years ago but to Console players it was a whole new world. What FPS on a console was any good before Halo? I would say the best was Goldeneye. The first Turok was descent. Pretty slim pickings after that. They just came out at the right time.
They also worked very hard to make the controls not only feel good but let you hit a target (which was pretty damn hard on other games before it).
I was a fan of the first one. I would play CS at work until 10pm, then stumble home and find my roomy had 14+ dudes in the living room having a LAN Halo fest. After a while I started playing and ended up having a great time. I think this was more because of the atmosphere then the game. It was great talking shit to the other team and getting all exited with your team when you won.
When Halo2 came out and it went online, the atmosphere was gone and I noticed I didn’t have fun playing anymore. The gameplay was just kind of boring to me.