Halo 3: ODST
It's worse than Reach. The NPCs can climb up boxes but you can't. It's very disappointing. No armor or shield. The health items are so small that it's hard to spot them. They tried to make a more story driven game, with a much slower pace. I appreciated the soothing jazz / blues music that plays in the city and the atmosphere of mystery. Somehow it reminds me of some tune from Parasite Eve, some flashback scene from FFVII and some anime.
The story takes place in the middle of Halo 2, when the Prophet of Regret travels to Earth. It's about rescuing a woman who has a secret piece of information that is crucial to win the war. I didn't find it to be much compelling.
I'd say that in my personal opinion, New Mombasa > New Alexandria. The environment art in ODST better communicates the story and better relates to the theme when compared to Reach. I didn't understand why New Alexandria was so clean despite the ongoing war.
The PC port wasn't well done because the whole interface has xbox controller's buttons.