This is essentially how I feel about Halo. I can probably count on one hand the number of discrete rounds I've played alone. It would be like eating a pizza alone. I've done that, too; not much there to be proud of.
The implication is there in the world, direct: the jeep has three seats, and you let them go fallow at your peril.
Reading over the reviews, I see it's still important to get your kicks in on ODST, even in a review of Reach, even though ODST remains a more robust narrative effort. Reach has segments that sing, standout hunks of gamecraft that stand astride the series as a whole - like the denouement that turns the classic jeep ending on its head, but as a coherent experience I still have to go with its predecessor. For a Bungie game, ODST was created under some comparatively firm strictures, and they needed to make a game that would fit the vessel. It's not an accident that it's the most compact, most personal, best executed story they've made to date. It happened because they had an editor - the most intractable, brutal editor possible, the only editor a company like Bungie need ever tolerate, that is to say the relentless march of time.
(The Fabrication Law that Brenna taught me goes like this: good, quick, and cheap. Pick two. That's from when she was a seamstress, but it's a very compact sort of wisdom that is clearly borne of exposure to the World-As-It-Is. But it's not as universal as it could be, because it implies that you have direct control over all three variables. It rarely happens that way.)
I was talking with my friend Sam Macbacawacha about the game a couple days ago, and he lamented the limited map selection. As an exercise in raw numerics, maybe eight isn't a lot. Generally speaking, people want more things. That doesn't necessarily mean that they'll use them, but n+1 is always the correct amount.
I listen to the album Guilt Machine a lot. Well, not the "album." I listen to the first track over and over again. Maybe I would like the other tracks as well, but I'm fine with what I've got. This, or the equivalent of this, happens in multiplayer games also. When you give me the choice via a traditional browser, I'll play the same ten percent of a game over and over again. I don't think this is a localized phenomenon, either. Dust. Facing Worlds. E2M1. Blood Gulch. You know these places. Unless there's a new gametype that requires a specific map, it doesn't change for most people. If you could play TF2's Payload on Counter-Strike's de_dust, believe: that's what people would do.
A million years ago, when I saw the reams of data they were collecting for Halo 2 at some Microsoft event, I overheard someone from Bungie talking about the Matchmaking having its own designer. Not UI, or engineering, or "experience," or anything like that: the playlists have their own designer. I didn't understand why that would be, but it's perfectly clear now. They calibrate the Great Machine - exposing every facet of the game though maps outside my comfort zone with gametypes that reveal them further. For PC enthusiasts, the Great Machine is the face of Goldstein - tyrannical and vile - but I can tolerate a tablespoon or so of tyranny in the service of my own enjoyment, for the purpose of dissolving ancient habits.