List 3 things with short explanations you would like to see in Halo 5, that haven't been mentioned often:
1. Better forge - make building pieces Forerunner, not UNSC, make flatter textures and normal edges with less bright colours, curved edges make for weird connections and magnets don't fix it, try prevent overlap glitches, corners are GOOD. Reach had good enough forge, all that was need was a graphics boost.
2. Talking Covenant? It was a good feature, they replaced with random noises, I don't know whether they actually spoke English before or if Masterchief's suit translated, but there is no reason for removing the feature plot-wise, adds some comedic break as well as possibility for Easter eggs, Halo 3 and 3 ODST did this very well.
3. Race Mode - This ties in with forge as it was hard to make good race maps with the new 'helpful' features. Completely left out, not only does it allow for a break from the normal shooting, it attracts people who are on the fence to buy Halo (I have multiple friends who bought Reach after I told them that) and it attracts people to forge, which also appeals to more people.
P.s. I'm not a Reach fanboy, but it was the best it could be for what it could use, except for the Revenant, that was just a garbage addition.