Despite the fear of health loss, because you have some rechargeable shield hitpoints to wear through before your health takes a hit, you can employ the same run out, unload a few rounds, duck back into cover technique that worked with Master Chief - just don't try to run up to a Chieftain with a Gravity Hammer and engage in some hand to hand action. This is something of a shame, really, because it means that if you're careful (and not playing on Legendary difficulty) health packs are rarely, if ever, needed, negating one of the biggest changes in this Halo over the previous titles.
Instead ammunition becomes the most valuable commodity. There are, of course, always plenty of enemy weapons to pick up from vanquished foes, but don't get attached to any particular weapon because chances are you'll be throwing it away in a few minutes. This is a minor complaint though because ultimately combat in Halo 3: ODST is every bit as brilliant as it was in the preceding three Halos (We all know Halo Wars doesn't really count).
That shooting Covenant foes with machine guns, laser rifles and rocket launchers is fun should be no surprise. But what's really important about ODST is what has changed. The majority of the game takes place through the visor of the Rookie, wandering the dark, moody streets of New Mombasa, your task to investigate the last known locations of your squad members. Interestingly, although the first two waypoints to which you must navigate are fixed, the four others can be tackled in any order of your choosing.
It's a similar concept to Wolfenstein - minus the Nazis - and it's all well and good, but once again it's openness for the sake of it. Bungie even admits there's an order that 'makes sense' in terms of the story, which is presumably what I got by sticking with the defaults because the plot seemed to make sense to me. I'm not criticising the concept of using New Mombasa as a hub world by any means, it's just a shame that Bungie hasn't made the order in which you tackle the various waypoints count for something - as it is it feels like a half finished idea.