LogFAQs > #961287790

It's definitely more than 9 hours. I put around 30 hours in doing mostly everything. Just haven't gotten all the collectibles and skulls. Certainly if you're really into the gameplay of Halo it's worth it.

The enemy variety is pretty good. The boss battles are the best in the series by default I guess, since Halo has never really done those well. However, they are also much harder than everything else in the game. On Legendary I died many times to almost all bosses. And from what I've heard, they're all still challenging on Heroic too. Difficulty aside, they're not too bad. All enemy AI is more aggressive in this game though, and it's even more notable with the bosses.

Vehicle combat is sadly quite bad. Most vehicles are far too weak. Warthogs are prone to flipping. The driving controls for the Scorpion are not easy to get used to. Marines also cannot drive for some reason. It's not too much of a blow though because generally you want to be driving them around armed with power weapons.