It's a fun game and I enjoyed most of it, but not without its faults.

First of all: Don't mistake my game time for actual time played. I got about 15 hours out of the full game with all secrets, expansions, golden skulls, etc. The other 115 hours are from trying to get the 66 hour achievement. Apparently the game uses a little secret in-game timer that only runs when you are playing the levels... would have been good to know, then I wouldn't have first waited 50+ hours on the main menu and then after it didn't work, I waited another 50+ hours in the first level, idling. Alas, none of that matters really.

But as for the game itself:

The story is barebones at best, but I don't think anyone is going into this with great expectations for the story. It works for its purpose and gives a bit of a thematic excuse for why it's in hell and there's metal playing.
The background music is really quite good and has some nice metal tracks that I found myself enjoying quite a bit. The rest of the sound is... okay. There's a few quips here and there which are okay. Bit Serious Sam-esque

If you are ultra competitive you will probably enjoy trying to get golden skulls and maybe high scores, some of the high scores are very suspicious though. However, there are some levels that have thresholds you need to get under that are simply not very fun to do (looking at you, B2) and might take you a few hundred tries.

For the most part, the game works fine, but there are some places here and there where movement doesn't feel... great. The jumping is a bit floaty and the hitboxes tend to not quite work as you'd expect sometimes, *especially* on moving level geometry, as if you keep some strange momentum that doesn't make much sense when you have air control and that you cannot cancel without landing. Jumping on slopes, especially if they move is almost random in terms of whether you will get some air or fall right into whatever is behind them.
I'm not sure if I'd recommend the expansions. The physics issues seem a lot more pronounced there and some levels really depend on you getting lucky with them, especially if you want to get those golden skulls.

Finally: Something I did quite enjoy was the great amount of secrets in the game. They range from collectibles to hidden QR codes (one of which reinforces my belief they took a bit of inspiration from Serious Sam) to other stuff. It's genuinely fun to find some of these accidentally.

In the end I did spend more time in the game than I had planned to, but the 15 hours I actively played I did enjoy a fair bit. :) Get the game on a sale though as it is kind of dated, and it's on sale often.

Not a good speedrunning game, they love to reset leaderboards