The game looks great and runs fine, and technically each mechanic is well-polished (that is, no bugs or obvious glitches that I've seen). But this set of mechanics just doesn't scratch any of the itches I'd want this game to scratch.
The game wants to be a rogue-lite / tower defense / top-down shooter / hero-shooter, and for all its great art, voice acting, and polish, it just doesn't succeed in my view.
The most consistent way I've found to win is to primarily use your heroes - treat the game like a third-person shooter. Turrets are too weak to handle waves without a ton of them and they cost too much to build a sufficient number.... So treat the turrets like small walls rather than your primary defense. You'll have to run all over the map with your heroes and almost every enemy will have to be taken out by a hero, but you start your hero near spawner #1, clear that out, then dash to spawner #2 where you built a bunch of turrets. The turrets couldn't clear the wave, but the monsters wasted their time clearing the turrets so your hero has time to run over and deal with them. Repeat.
I just don't find the above fun. I wanted the strategic placement of turrets to take center stage, and have my heroes run around fixing turrets and maybe dealing with one or two enemies that slipped by my defenses... But again, this isn't really a tower defense. At least, I haven't been able to make a tower defense strategy work.
It wants to be a hero shooter, where you play characters with special abilities. Kill a lot of enemies to charge up an ability, then unleash it. After killing ~20 enemies, my character can charge up a short-range cone that.... slows enemies for a few seconds. After killing 40, they can use their ultimate ability in a short range around them that... knocks back and slows for a few seconds. It was always better to just keep shooting.
It wants to be a roguelite, but the customization options are lacking both in breadth and depth: There are very few to choose from and none of them are remotely game-changing: you move a bit faster but have lower defense. -10% attack damage, +30% crit chance. These might be fun if you could stack them, but you can't. Only one per character.
It wants to be a tower defense game, but the turrets you start with have such low range, low defense, and high cost that you can't make more than a handful: They only get a couple of shots off on a monster before they get hit because of the range, and they need a hero constantly next to them to repair because of the low defense... the problem is, my hero's auto-attack does so much more damage and fires so much more quickly and has so much more range that if I have a hero next to the turrets I'll kill everything coming at my with my hero's gun before anything gets in range of my turrets. So... If you have a hero next to the turrets then turrets aren't necessary, but without a hero nearby to repair them turrets go down too quickly, and because you gain resources by opening doors and expanding the map, you can never build enough turrets to defend anything... The bigger the map gets the more you need to defend, but you only get resources to build turrets by making the map bigger. All in all, this was the most disappointing facet of the game to me.
Finally, it wants to be a third-person shooter - and this is the one thing it actually is. If you want a satisfying isometric shooter, this might be a good game for you - especially if you have friends to play with - but even then the presence of the previously mentioned mechanics are all the game has to make it feel replayable, and they just didn't work for me.
I saw the mixed reviews and thought 'okay, people played Dungeon of the Endless and this game was different so they didn't like it, but I'm okay with a game being different, I'll give it a shot' - I was disappointed.
There is a good game in here if they fix it up, but for now I'm trying to decide whether to push forward and see if maybe I just haven't learned how the game works or whether I should refund it, and honestly for the $30 price tag, I think I'll just refund, I'm sorry to say. I hope they fix this game because you can tell they weren't just phoning it in - the game looks gorgeous, character designs are unique, lots of voice acting and a TON of polish... It really makes me wonder if I'm not getting how the game is supposed to be played, because clearly the people who made this had a vision and it feels like they made what they wanted to make... But I just don't find it very satisfying.
As a last note, what I'd love to see is something like this:
Increase turret range and defense so well-placed turrets can actually kill monsters.
Increase the number of monsters that spawn so that you HAVE to use turrets and can't just fight everything with your heroes.
Reduce the effectiveness of hero auto-attacks so that a hero's time is better spent running around repairing turrets (for those who haven't played, you just run up to a turret and melee it to repair it - one melee restores almost all of its health, the repair process isn't tedious at all).
Increase the number of ways to modify your heroes and give us something that isn't just "+X stat, -Y stat"
Tweak the resource cost of turrets as needed.
Add a tutorial for researching/upgrading turrets at a research station.