Quick impressions so far. Playing on Heroic and haven't found it particularly challenging.
Graphics.
The visuals in this game are so unbelievably inconsistent. It can go from wow that looks incredible to holy shit that looks terrible, within moments of one another. But Reunion is the Mission that has really finally kept my mouth consistently agape in appreciation and awe. Reunion is not only the best looking mission so far, but also the best paced in terms of gameplay too. Slower paced, slightly more methodical, and overall more classic Halo feeling (only not so sandboxy).
Summary and issues.
Overall I'm definitely enjoying the game a lot, but it hasn't completely grabbed me. Some of the pacing, and certain elements just seem a bit rushed or cobbled together. The characters and story a bit here and there, and I also find (unless I'm going crazy) that Locke controls ever so slightly worse than Chief, as if there's added movement sensitivity or speed or something. I also find his visor a bit overbearing, which coupled with the field of view can sometimes make things feel a bit too in your face, especially when climbing or hopping around. For whatever reason, Chief's visor feels ever so slightly less cluttered.
The friendly AI is also really bad. They have done some pretty dumb stuff so far in my campaign, and when it goes from cut scenes where they're kicking all sorts of ass, to gameplay where they're straight walking in to or shooting walls, it's a bit jarring.
One other issue I've had is that the aim assist can sometimes be detrimental rather than advantageous, especially when it pulls your reticule away when enemies cluster together or run by the person you were aiming at, making it harder for you to get the head shot on your initial target.
Positives.
The main thing that makes it for me are the weapons in the game, many of which are super satisfying and diverse in feel and aesthetic. There's also a shit tonne of them, and it's interesting to just experiment with them.
The vehicle segments have also been fun, though not quite as open as I might have liked. I haven't really been able to just let loose and throttle it with the Mongoose or Warthog yet. In the segments they've been in use, there's usually constraints, obstacles or barriers never too far away, but that doesn't stop them from being fun to use either way.
Lastly, I'm definitely digging the added verticality in this game. Whilst it can add it's own situational dangers, as there's more places you need to watch out for, it also gives you extra freedom in terms of manoeuvrability and vantage points, and it's sometimes cool to just climb and jump about searching for new weapons in the midst of firefights.