The ODST are an entirely volenteer corps. They're also the best of the best. The SPARTAN II project made 75 nutters who were smarter than any normal soldier could aspire to be, they also had no sex drive to distract them, not to mention all the other augmentations. 4 spartans would take out an entire covenant groud invasion. UNFORTUNATELY, Bungie didn't feel quite comfortable giving their Halo fanbase a game in which combat was actually fast paced, so they decided that they'd give you the MC with a larger health bar. This may have been due to budget and time constraints, or it may just have been them passing up an excelent oppurtunity for some kind of guerilla warfare game. BUT, Halo's fanbase is mainly comprised of people who don't have time for tactics, ambushes, or anything other than runnign up to try and get in the first melee, so in retrospect, ODST being what it is makes perfect sense. Even if it IS an affront to actual gamers.