From a gameplay perspective, they should never have added armor abilities, sprint, loadouts, perks, ordnance, and instant respawn. Halo was an arena shooter and those things do not work in an arena shooter.
THAT is something that should have never changed, and when Reach tried to change the community lashed out and the game died quickly, much like Halo 4. I understand that some people enjoyed Reach/4, but there is no denying both games flopped/are in the process of flopping.
You’ll notice the Halo games that changed the least were the ones that lasted the longest and were generally well accepted by the community. I’m not saying change is a bad thing, but when you try to change too much(Reach) or just for the sake of changing(4), you’ll get bad results as you can see.
What the developers should have done was smartly expanded upon the Halo 3 formula. I hate it when the defense force tells us that we just want a Halo 3 clone, because that isn’t true. We know it worked, and it had areas that could be improved. There’s no point in trying to expand upon a fundamentally flawed design philosophy. Halo needs to return to its roots. People bought Halo because it was Halo. It was popular because it was Halo. Now it feels like some watered down COD with shields, and if I wanted to play COD I’d just go play the real thing instead. This is why it’s bad when you try to mix different game styles when you already had an established style.
Halo was Halo, COD is COD, Gears is Gears. Let them be what they are instead of trying to mix them together.