Halo really is over rated. The level design on single player is really bad and repetative around the middle of the game through the end. Multiplayer is ok, but there are no extra modes I have found that you can play alone, which is a bummer. The only multiplayer map I really like is 'Hang em High'.
I thought MP was over rated when I started playing it too. I got it, played it for 3 1/2 hours, was going in circles, and quit. 4 months later I gave it another chance, and found where I was suppose to go (instead of in circles). From there it was smooth sailing. I got all the upgrades, the puzzles and bosses are great have awsome use of weapons and power ups. Its now my favorite game.
Although I did have to cheat with an FAQ to figure out where to go initialy (and get out of that damn circle). But whatever it takes...Its a good balance of freedom and restriction, you can go a lot of places but eventually your gunna be locked out of them all and only have one option that will lead you to the weapon that will open up the doors you were locked out of.