this game is awesome nothing more nothing less
I won't really comment on the core fighting mechanics, as it's pretty much the same as Halo 3 with some slight tweaks to fit the new setting. Weapons feel familiar and your inability to dual wield (which actually cleans up the fussiness of fiddling around with dropping and picking up weapons to get a dual-wielding layout) is really all that's new when fighting.
The twist (at least for the Halo franchise) is that you are a "normal" human now so you need health packs, and though they are sprinkled around fairly liberally, it does require you to use more strategy instead of charging headfirst into battle. I tried to play it like I was Master Chief at first, but after the first act you pretty much adjust to your new limitations.
The way the story unfolds is rather great - it's an out of sequence narrative where you slowly piece together the adventures of your fellow ODSTs as the initial drop goes haywire and everyone is spread about New Mombasa . I won't give anything away, but it is a nice change of pace and really adds to the richness of the characters. Also, it seems like the whole cast of the now defunct Firefly television series does the voices which further enhances the power of the narrative. I hope Bungie keeps a narrative style similar to this game in the future, it's really done well.
I've only played the single player story so far, but safe to say, if you are a Halo fan, this is THE Halo to get. I'm glad I did and it's really renewed my love for the Halo universe.