Well i got H3 ODST a few days ago, i already beat it on legendary, got all achievments that i can get offline and ive found almost every secret there is..
Well its a good game, and itll take a few days to complete if you play it like i did. Getting a CD with all the H3 mappacks though, that is kudos! =D
Anyhow The campaign is pretty decent (i luv that you can see "in AmberClad" fly into the slipstream with the covie assault cruiser) It gets a good feel, sneaking around mombassa, dodging brutes and sniping down jackals.
It has quite a few referals to Master Chief, you can find BELIEVE painted on walls almost everywere and under many of them the numbers 117 have been drilled or shot into the wall (maybe refering to how players sometimes write on walls by shooting in Halo 1-2-3). I have also found numerous grunst screaming DEMON! to me, but thats only when IWHBYD skull is active (btw why the hell do you gt to start with all the skulls =( i luved skullhunting!). Also one thing that shows that they have made ODST by modding H3 is that they have forgoten to change the camera hieght on the player you are, so your a good 20cm taller than everyone else (maybe just 10cm). Plus ODST cant handle bruteshots or gravity hammers, but ROOKIE CAN! (maybe hes a mutant berserker ODST)(and marines usually cant melee down a brute right? maybe if theres 10 marines kicking him, but seriously, bungie must have had one heck of a rush on ODST because there are quite a few things they could have done better)
Okay enough rabling, to sum it up, if you want a good weeks halo gaming its a good game to get, then you can also forge like hell on the new maps (mmmmm Sandbox and Orbital ftw!)
Okay thats my short long review for Halo 3 ODST, i will make one for ME2 soon