The Animation and the Music are just beautiful. And if you've read anything at all about the game you heard it's tough. And it is. Cuphead is essentially a series of boss fights you can select from an overworld map. With the defeat of each boss, you unlock more of the overworld, and you can find more boss fights. There are a few non-boss fight levels in the game (six if you're counting) where you run around, shoot things, and collect coins, but mostly this game is all about the boss fights.
So whether you consider this game good or not will really depend on how much you enjoy the boss fights. I've heard a lot of other reviews saying that all the boss fights are 'tough, but fair'. That is a lie. Most of the fights are exercises in overcoming frustration, learning patterns, and hoping for some good RNG so you get patterns that won't hose you. That anyone thinks that the fights are in any way fair are a testament to just how charming this game is.
Some of the needlessly frustrating things I've found with this game is how a lot of time objects that can hurt you are obscured by set dressing; Bullets hidden behind foreground detail means hidden surprises to sap your life bar, and losing one of your three hit points to something you literally had no idea was there sucks. On some stages you need to ascend platforms to avoid projectiles and other hazards, but where the platforms appear seems to be generated randomly. I often found myself in spots where there was nowhere for me to dodge without taking damage because of dumb luck. Also, on the overworld map there are hidden coins you must find (if you want to buy all items and get 100% completion), but save for one coin, there are no indications where they might be. You need to either hit every pixel or look at a guide to find the coins, and that just rubs me the wrong way.
But these are fairly minor gripes. The game is charming, if difficult. If it's your sort of thing, then you'll like it, but know what you're getting into.