The only playable level is Delta Halo but even that one sucks compared to Halo: CE and Halo 3's levels.
Halo 2's levels are mostly dark and full of flood. And you have to play as the enemy 50% of the time which makes it even worse.
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Agreed. I think the storyline was pretty cheesy and the AI flat out sucked. It didn't have the epic feel that Halo 3 had.