If you have'nt heared the news, Halo : ODST has been released today if you are intrested in buying the game it may be around £/$45 maybe £/$50+ if you buy the bonus pack aswell which is you are able to play Sgt.Johnson . The game is a major release. There are previews on Youtube.com for the 1st misson which I have seen I will give some info on the game but not to much because that would just ruin the entire game for you. You are a ODST (Orral De Shock Trooper) About to drop down into a covenat ship but the ship gos lightspeed and you and your team go off course which is leading you to a planet where I don't know but you may be the only surviver from the crash of the squadrin.
Note: You do not play 'The Master Cheif'or any other Spartan class you are a regular human and you must go to health points (I think so) To regain your health (Not sure but confidant) I'm soon to be pupishing the game and if you would like to know more Info on the game request here and I will gladly tell you Yours Sincerly Tom
For fututre reference, firefight its like horde mode from gears, but bungie had planned to introduce it in the original halo 3 but they didnt had time to introduce it.
It is "like" horde mode, but a lot damn harder.
especially when you make it past the 4th set (60 waves, 2-3 hours on heroic)