Firefight is starting to grow on me. The first two rounds are all action and mayhem, and celebrates Halo 5's gunplay and movement. Its full on hectic infantry combat, jumping and boosting with your team. Feels great.
The later rounds things get more bullet-spongey, and ammo becomes a serious issue, and if you aren't busting out the bigger REQs -- assuming you have them -- you're not likely to get very far at all, and even then you're very likely to get insta-killed from a variety of enemy power weapons with splash.
My wishlist after a smattering of matches:
* More warning when Prometheans are about to teleport right on top of you in quantity. Most of my deaths have come from this. An empty area that five seconds later is filled with half a dozen crawlers or even battlewagons. There's just no surviving that.
* More ammo. The player's ammo capacity doesn't at all square with the number of enemies you have to face, and how tough they are to take down, and how far they tend to be from REQ terminals. This mode would play so much better if I didn't feel so tethered to the REQ terminal even with basic objectives.
* Speaking of being tethered, this mode could use some kind of secondary spawn control objectives. It sucks to spawn back in the game and have a huge hike ahead of you, and it happens often enough that popping vehicles on every spawn isn't going to keep up with need. Maybe players that aren't necessarily tackling the primary objectives can still unlock closer spawn points to help the team or something along those lines.
TL;DR: The action is great, the spawning and ammo could really use some love.
Edit: I did run into some weird ass audio bugs. Most of the time I can only hear Palmer giving her intro on match start - no music or other effects until players are on the ground running.
The weirdest bug/glitch/whatever is when I can hear audio that seems like its from players talking in other matches, or even announcers live-streaming play by plays, even after muting all players. Don't know what the hell is going on there but it happens strangely often.