Halo 5 on top. Halo 4 on bottom.
Am I delusional, or does halo 4 look superior in detail and in lighting? I know halo 5 is still unfinished at this point but... The difference is striking.
Are you kidding? No way. From a technical perspective, the H5 shot appears to have way more going on, more light sources in general, note the way the light's affecting the visor and even the top of his helmet, etc. While in Halo 4 it might be a more "natural-looking" or "smooth" light, it's using considerably less light sources and is basically just the background lighting and the single light source from the Energy Sword lighting up his whole suit.
I wasn't going to bring it up until I saw some actual in-game screens, but based on everything I've seen so far it looks like they've basically combined 4's high-level-of-detail aesthetic with the cleaner textures and brighter colors of Halo 2 Anniversary, and it looks great. The smoother armor in that H5 shot almost reminds me of Smash 4 or something.
EDIT: to clarify, beyond the lighting - there's obviously more polys and more potential for stuff going on in the H5 engine, but the reason Chief looks "less detailed" is because they deliberately dialed back a lot of the more baroque textures like scratches literally everywhere on his armor. It's a welcome choice, imo.