Been struggling with understanding the appeal of Halo, and I think Halo ODST saved me from completely abandoning all interest in the franchise. First Halo was cool in its day and I enjoyed it (a year after its release on my Mac) but Halo 2 and Halo 3 even did little to nothing for me. For me the whole trilogy lacked in any tactile sensation for me whether it was Master Chief's super floaty jump or the plastic pellet gun sounding sound effects (silenced or otherwise!). Story-wise it was mostly go over there and shoot. Very little dialogue and Master Chief's silence felt weird during most of the game. Conversely the military marine talk got  tiresome and sounded forced.  
 
In ODST though, the tactile sensation I craved is mostly there. I think the sound effects still suck, but the layer of grime in New Mombasa and the sense of loneliness and quiet exploration is a lot more interesting. I don't know what's happening or what I will find around the next corner and that's what I love. Plus the ODST helmet gear has all the stuff I figured Master Chief would also have like the ability to set waypoints. The relative squishiness of the ODST characters, their vision turning read, the beating of their heart and the grunts upon losing stamina go a long way to making the game feel more real. I'm realizing what it was that the Halo trilogy was missing and this gives me much to look forward to in Halo Reach.  
 
If they make a Halo 4 though, they'll have to convince me they've learned to direct cinematic cutscenes, use music dramatically, and write/voice dialogue before I'm willing to follow them down that path again. Halo universe good, Halo shooting mechanics good, Halo storytelling weak. I just wish the ODST storyline was longer because I'll probably be done with it very soon.