This may only feel like a Halo 3 expansion for some, but ODST has a lot too it for all Halo fans and story lovers.
The story is not about Chief this time, rather it is following a squad of Orbital Drop Shock Troopers, dropping down to earth when a Covenant ship jumps into hyper space in the middle of the city, throwing your whole squad off course. You wake up 6 hours later at night, getting out of your pod and finding the city in ruin. It's very quiet in the dark, nearly empty city. ODST has really brought immersion into the storytelling. You are searching for your team and when you find items you play a mission, which are flash backs of what happened to that person. When you are searching for those items you are alone in the dark city and it gives you time to think about everything which other Halo games never did. The story is good, not revolutionary, but you get to know multiple characters in the squad and the setting works really well having to find your squad after being knocked out.
The most exciting addition to ODST is the new mode Firefight. In this you fight wave after wave of increasingly harder enemies while gaining points. You have a set number of lives which you can gain more by surviving rounds. You can do this with three of your friends, so like playing co-op campaign. The maps created for this work great and the whole experience is very addicting. I played more Firefight with my friends way more than I just played online. There is no matchmaking for Firefight, so lets hope you have at least three friends with this game!
Gameplay feels just like Halo 3, but you aren't as strong as Master Chief, so you can't jump as high or take as much damage. Health packs are back after only being in Halo 1, but your shields drop very fast and your screen gets red a lot and it gets quite annoying.
This probably could have come as a big DLC, but Halo: ODST is very much worth getting, witch its great new and different story and new game mode. It is still that great Halo experience and a great time with friends.