I played a handful when I first got it. Played a handful when an old Halo-playing friend was in town for a bit. I thought it was fun with people, and I liked the mode where you have to capture bases and build guns and vehicles. But overall I found it too fast-paced and frenzied, and found the menus/lobbies confusing.

I didn't mind unlocking guns and loadouts, though I never kept track at three or four numbers... XP , levels, SP? Couldn't quite figure out the point of them all. Other than the guns and the abilities, I wasn't interested in the armors. They all bled together for me and either were over-designed or just didn't feel like Halo. Some of the maps were pretty cool, but some of the Forerunner levels were hard for me to navigate or focus on and understand dimensionally, as all the lines everywhere confused my sense of space (had the same issue with the campaign).

Went back and tried Reach for a little bit recently. Definitely more my kind of pace, and the gameplay areas were much more clear in their and understandable in their design. But if someone came over to my house and said they wanted to play H4, I would not oppose. :)

Halo 2 and 3 remain my sweet spots (and about only spots) for competitive multiplayer fun in my gaming life. I usually prefer cooperative and immersive experiences.