Anyone who doesn't like Halo based on the fact that its levels didn't look OMGAWESOME and that the enemies don't have perfect AI can just shut up. It started in what, 1996, 1997? Ended in 2000? I'd say for that long, they made a helluva game. That's still everyday by hundreds, if not thousands or MILLIONS of people every day. The PC version blew for all intensive purposes (crappy netcode, no co-op, rocket warthog (wtf?), flamethrower), but the X-Box version is gold. It's the second FPS I ever played that was MADE for a controller (the first being Goldeneye). I mean most of the time I ask people how the PC version compares to the X-Box version, and they say that it doesn't. The X-Box version may not be graphically on par, but damnit it's way more fun. And this is coming from one of the most hardcore PC gamers you'll ever meet.
Either way, though, if you think Halo's level design is bad, you've got something wrong with you. If you notice the levels that 'all look the same' are all in the same area, made by the same race. I'm not sure if you're aware of this, but oftentimes, people follow architectural patterns quite often. Down to a T even. I thought the level design was plenty fine.
Either way--Halo 2 will be badass, it has no 'mistakes' to make up for, but it will definitely improve on the mediocre things that were in Halo, though I'm not looking forward to the new tank. I just hope that their PC port isn't so crappy as the last one.