Mediocre shooter with the name "Halo" in the title.
A lot of Halo 3: ODST apologists say you can't really criticise this game because it was "never intended to be a full-fledged sequel." Well, if Microsoft released ODST as a $20 downloadable add-on for Halo 3, that statement would certainly ring true. My take on it would be: "ODST is a solid expansion and a serviceable shooter that features Halo's great combat mechanics in a welcome new spin on a well-worn formula."
But unfortunately, Microsoft did not release ODST as a DLC add-on. They released it as a $59.99 standalone title with maybe a 4-5 hour single-player campaign and one new mode to online multiplayer. I'm not much of a fan of console multiplayer shooters, so I can only comment on ODST's thin single-player content. Bungie definitely brought a welcome new mature feel to the storytelling this time around, with much of your time wandering alone on the dark, desolate, post-invasion city streets of New Mombasa to discover the fates of your squadmates. Most of the city feels a bit generic and not-quite-futuristic enough, like a third-rate copy of Bioshock's "ravaged city" in Halo's sci-fi shell, complete with uninteresting "audio files" sprinkled around the town.
The main storyline levels, triggered by finding leftover artifacts from your teammates, are much brighter in the traditional Halo sense, but feel small and unambitious in scope, especially compared to the incredible level design on show in Halo 3. Your teammates' personalities are fleshed out a bit more than usual for a Halo game, but they're all still forgettable cutouts, even the central duo who share the game's main plot focus. The overall storyline isn't much to get enthused about, even for Halo's mediocre standards of science fiction.
On the plus side, Halo's combat mechanics are still extremely fun and a few "Defend this spot!" missions get the blood pumping as you beat back wave after wave of Covenant.