You start marketing to a different demographic which both Halo & Call of Duty have clearly done for a while now. I'd much rather have more of a hardcore, more realistic Halo experience. I also wouldn't mind Call of Duty going back to more of war style game which all of them were up to World At War. Now they are all about making an "action movie" experience in the campaign instead of more open gameplay. I still remember playing CoD1/expansions/CoD2 on PC, those were great experiences fighting along the endless stream of troops that came in to fight with you. Now it's not a war game, it's an action movie game marketed directly to 12-18 year olds when before it was marketed to 18-25 year olds.
Halo:ODST was probably the worst $60 I spent on a Halo title ever. Halo:Reach was so hyped up saying, "Oh, this is our going away present to fans" and outside of the slightly above average campaign, that game was a turd online, everybody knows it. Then H4 was a decent step back in the right direction, but the gameplay was basically trying to mix CoD/Halo with slightly storybook colored graphics. Still, H4 was probably the best one released since H2 honestly. H3 sucked, the gameplay was slow, the vehicles were slow, and the map design/gameplay was terrible. The maps really took me out of H3 minus 2-3 of them. The whole Bubble Shield/Health Regen thing...that wasn't even needed at all.
All they really had to do was make Halo 2 again online with that quality of maps & gameplay while tweaking small things & adding slightly to it & everybody would love it. I mean as far as making sequels. That's their problem though, they always to try fix what's not broken then they hire a bunch of people that don't know how to make quality games anymore or fun gameplay from passionate designers like Halo 1/Halo 2 was. They expanded & hired a bunch of programmers at Bungie, key people left, then MS's marketing took over. That's what I'm talking about. It's fine if you disagree, but that's exactly what happened & I felt like the quality of the product has suffered since H2. I don't think I'm the only one either as most gamers have all but abandoned Halo online now.