I played 4 several times at a friend's house but haven't bothered to buy it since I don't have Gold anymore and so wouldn't even be able to play Spartan Ops. Also because I hated the game. No reason to waste my money on something that I'm not even going to play.
Why? I can barely play Halo: Reach now, after playing TMCC for so long. It looks so pixelated and the fps looks terrible. I didn't expect 1080p/60fps too look so different, and at first they didn't but when I go back and compare them, the difference is massive.
I'm actually in the same situation as you. I haven't played Reach in a while. Now I'm always switching between 3 and ODST, and sometimes CEA - which I consider better games. Reach's story felt so underwhelming.
I liked Reach's story. Not nearly as much as 1-3, but it was a much more human story. Like CE and ODST it kept the aliens mysterious and evil, like predators from the Predator series. Reach's story was arguably more low key and sad, but it explored the human side of things. We never got to see a colony before, and rarely saw civilians in a Halo game. And wildlife, that was a great achievement. And shoot me if you want, but Reach's firefight was better than ODST's.
Mindless apes? In ODST, they spoke English and had modern armour; they were organised and competent. In Reach, they spoke an incomprehensible language and had almost no armour, which made them act more savagely. They were constantly charging at you with their Spikers.