Just got the game today and loving the shit out of it. Played from the beginning through the first Hell level in one sitting on Ultra-violence.
The combat is so white knuckle, like holy crap. Stand still for a few seconds or get cornered against more than one or two enemies and watch your health melt. I immediately switched my controls to bumper jumper (Strafe) and proceeded to bounce around arenas like a madman, bunny hopping all over the place while slaughtering my enemies. I'm also loving how varied the fights are - arenas that focus on verticality with not a ton of cover, arenas that focus on one plane with an abundance of cover, and everything in between - not just because of the arena layout variety, but also the enemy variety. Imps move around like crazy and sling projectiles from every which way, Hell Razers try to snipe, Knights rush you down for melee, etc. The use of power ups is also excellent, with even a single one potentially adding a ton of strategy to fights. The last fight in the Hell level I played kicked my ass a handful of times, until my best use of quad damage yet sealed the deal. Outstanding combat. Few action games have me pausing after a fight and thinking "holy shit, I just fucking did that".
I'm also being constantly surprised at how engaged I am with the downtime. When combat is on, I'm highly engaged and fighting for my life. When combat mode switches off, I find myself remaining at a high level of engagement looking for secrets. Not only are they satisfying to find and often well-hidden, but they yield huge benefits. While not every weapon mod is a winner, every weapon seems to have at least one mod that dramatically impacts combat, and every single secret contributes to powering these mods up. I probably spent 20-30 minutes running around the second level, having cleared everything else out, looking for one blasted secret I missed. I eventually found it after some serious Metroid Prime-ing, and it felt pretty damn good. No autopiloting through the downtime in this game. Barring the occasional short first-person cutscene (blah, but it's a 2016 video game), the game has me in the zone at all times. Just how I like it.
I didn't even mention the killer soundtrack, the platforming (Space Jump boots!), or how nice the game looks despite running at a nearly locked 60FPS on PS4. Not sure what else to say...game is just a ton of fun, and exactly what I needed right now after, uh...a certain other game. Hopefully it holds up!