The trailer looked great. The new engine looks impressive, and I'm glad that 343 Industries is returning to a more old-school Bungie-influenced art style. But I'm really hoping that Halo Infinite has more going for it than just looks.
I hope there's larger, more expansive levels in Campaign, and that it's overall the largest campaign to date. While Halo 5 did have level designs that offered more ways to approach combat, those levels were still relatively small. In fact, Combat Evolved still holds the record for the largest Campaign stages that doesn't require a vehicle to complete: Assault on the Control Room and Two Betrayals. Nothing else comes close to that kind of scale except for a handful of missions later in the series that were obligatory vehicular sections (e.g., the Warthog runs, New Alexandria's open airspace that required a Falcon to traverse, the space fighter segments on Long Night of Solace and Midnight). While I don't want an single open world, I do want levels that are big, open, and have plenty to explore. I still remember spending hours checking out every nook and cranny in Halo CE and even Halo 2 to an extent just to see what was there and if I could. But over time the levels in Halo campaigns have trended to be more constrained, with more artificial barriers to exploration and going off the beaten path (e.g., invisible walls in easily-accessible places and kill barriers both hard and soft). A "spiritual successor" to old-school Halo would try to bring some of that back.
I also hope there's a lot more on the multiplayer side as well. Among my complaints about Halo 5 was that the roster of maps was very sparse. There are noticeably fewer regular developer-made Arena maps than in any prior Halo game, most of them are paired "remix" maps that are thematically similar, and none of them are Big Team maps. 343I have been incredibly dependent on Forge maps (which usually don't look or play as good as dev-made maps) to pad the map roster. Overall, Halo 5's selection of maps is very lackluster and limited, and Infinite needs to make up for that with a good selection of maps, at least 15 4v4 Arena maps and a half-dozen or so Big Team maps. Also, there were many classic game modes present in older titles that were flat-out eliminated in Halo 5 and required jury-rigging them with Forge scripts to somewhat replicate. All those gametypes should exist right at the beginning in Infinite, without needing Forge scripts to recreate them.
Finally, if this game really is a "spiritual successor" to Combat Evolved (and the original trilogy more broadly), then it needs to be that more in just terms of setting, atmosphere, and visuals. The gameplay needs to be brought back to something more distinctly classic than Halo 5's. "Spartan abilities" made for a much faster-paced Halo (a pace I still can't get used to), but Halo was never about fast-paced twitchy combat. It traditionally had a slower, more deliberate pace than most other FPSs. The core abilities of the Spartans need to be pared down to the basics, making them more like "walking tanks" again instead of the "fighter jet" style 343I was going for in Halo 5. Instead, combat should be evolved through focusing on things external to the player, such as the weapons, vehicles, environments, and (for Campaign) enemies. Evolve the sandbox, not the player's core attributes.