10/10. I LOVE this game.
For me, this game hits a total sweet spot of awesomeness.
It may seem odd, but I'm going to compare this game to Tetris, as a lot of the positive characteristics of this game are in common with Tetris.
Like Tetris, you can very quickly get into this game. Within seconds, you are playing the game, and learning the game from experience. You don't need a manual (though you will probably want to do some reading after you get your hands dirty for awhile). Just get in there and play!
This is a skill based game. So much of the reward of the game is in realizing that YOU have leveled up, and learned to overcome challenges that initially seemed impossible.
It's all about the gameplay. There is something zen about the experience (something I got with Tetris, too). Just shooting at stuff and dodging all kinds of crazy attacks... it sucks you in.
It's a game that doesn't require absurd committment. It's not a deep story or deep world. You can pick this up and play for 15 minutes and put it down.
It's SUPER replayable, owing to the randomly generated levels and the huge variety of characters and level up abilities and weapons and so on.
Aside from that, this game just rocks. Just as an example, the weapons FEEL GREAT. The guns have real weight and power to them. It's a joy blowing stuff up with explosives, or whacking monsters with melee weapons. You will feel like a boss wading through levels with your guns blazing.
The game is also very comical, and absurd things happen all the time (crazy unintended consequences owing to all kinds of powerful weapons and powerful enemies.
The game rewards experimentation and careful strategy. It's a joy to learn all the nuances of the game. Pit your skill and your knowledge against a very challenging game.
It is a hard game, but I personally found it to be fun at every stage. I highly recommend this. One of my all time faves.