I guess I can't blame someone for being unimpressed, if they just blazed through the game in Normal mode. At that difficulty, the things that make Halo fun and unique don't really make a difference. You can just blast through with the assault rifle, never perfecting your grenade tosses or finding cover. If you did that, it wouldn't seem much better than any other shooter.
The battle lines are drawn, I guess. Bioshock will be the rallying point for people that care about story/atmosphere/presentation, and Halo 3 will be for people that enjoy detailed gameplay and scenario design. Which is sorta what burns me the most about the snotty, unsubstantiated "2001 gunplay" snipe -- Bioshock's gunplay doesn't strike me as anything we didn't already see before the turn of the century.