I played this game on stream: https://www.twitch.tv/videos/1832466938?t=01h34m13s
I'd played this game in the last Feedback Quest, and I think this version is much better!
I had fun, and almost killed the first boss multiple times (got really close once).
One thing that definitely stood out: the game is a LOT more vulgar that I'd thought. When Mike was talking, he starting cussing, a LOT. I'm glad I was wearing headphones since I wouldn't want my kid to hear that.. considering the graphics of the game and the overall feel, this was incredibly surprising. Maybe have a way to toggle vulgarities, and/or censor the sounds/text in the options? I also noticed that the player would say "damn it" during the game quite a bit, which is not as vulgar.. but something I'd also prefer my kid didn't hear from a game.
I think I encountered a few bugs in the game: when I was playing the hunter, after each level, I didn't get a level-up gem selection thing, compared to when I was playing the defender. Also, at one point, the portals didn't close after each level, and the progress bar on the top wasn't progressing even though new waves were spawning.
The difficulty of the first 2 levels are great, but I think the first boss fight might be a little too hard? I tried that level a number of times, but never managed to kill the boss, even after purchasing upgrades. I can imagine a player getting frustrated at that point, so maybe tweak the difficulty of the boss fight down a bit for that level? I can't speak to the other levels since I didn't get that far.
Regarding the upgrades, one possibility is to allow players to refund their purchases. I spent 45 red gems on unlocking the Hunter, but when I'm playing the Defender, it feels like the 45 gems were wasted. While gems aren't that difficult to earn in-game, it would have been nice for me to "respec" my options.
I really loved the banter that Mike would have in between games. It adds a ton to the lore and feel of the game. I think the game would feel very different without Mike's character, so keep it up (except maybe less vulgar :)