It's my favourite Halo game, and I am a Halo fan. I love the atmosphere, the open-world (even if it's copypasted street segments), the audio file collectibles, almost everything.
I do think it was kind of lame to start it off as an expansion and then ship it as a full game, and I do think it should've been less than full-price, but I love it so much I ain't even mad.
I had a few qualms, of course: Considering it was supposed to be a campaign only type thing, I wish the campaign was longer. And since it grew out of being a campaign-only thing, I kind of wish it had competitive multiplayer (it was cool that they included the entire Halo 3 Multiplayer, but having already purchased all the previous DLC, it wasn't too amazing for me).
Also, the stealth was shit. There's no denying that. They gave you a silenced SMG (had a scope, awesome) and the "whisper-quiet" Automag (also had a scope and could fire as fast as you could pull the trigger, awesome), and yet the moment you shot, everyone knew where you were. Stealth has never been Halo's strong point, unfortunately. Also, the Automag was definitely a headshot-capable weapon, it amounted to very little to any enemy with any sort of defense. Also, and this is something that irritates me with every Halo game, the Sniper Rifle of all things is hardly headshot capable. I like Halo's multiplayer, where a headshot is a kill; not so much the campaign, where a headshot equals knocking off his helmet and alerting everyone to your position. Why doesn't it kill them? And why wasn't it silenced? Come to think of it, why wasn't every weapon in ODST (every UNSC weapon anyway) silenced?
Firefight is fucking awesome, way better than in Reach. Since you can change the settings in Reach to be identical to ODST, simply being weaker/ making it more challenging isn't why. I think it has more to do with the enemies, weapons, and maps. The maps are just more playable, the weapons are more fun to use, and the enemies offer unique challenges. If an Engineer shows up, you take out the Engineer or you are fucked, because they give everyone else health and shield bonuses. If the Drones show up, you whip out whatever automatic weapon you have and run for cover because they fly erratically and rain death.
Captcha: boom stick. Rather appropriate.