Do you like guns? Do you like Pixel games? How 'bout dungeon crawling? What about roguelike? And what about having moments of agony for loosing focus on a good run and failing because of it?
If all your answers were 'yes', then you might like Enter the Gungeon. WELCOME TO BULLET HELL (kind of) .
Enter The Gungeon is really good for making player to go further and further, and to challenge youself too. In every Chamber there will be new enemies with different weapons/attacks, abilities and different quantities of traps. Game offers you four main characters with their own unique abilities to play as and to complete their side of the story in ETG.
Depending on the run you're having moments of easy can make quite fast 180° turn and get you overwhelmed. Only learning from your mistakes and learning the enemy patterns you'll succeed... or you just have the most dumbest luck and get through the game with easy, that's possible too.
Even when you get passed the " Final Boss " you still have things to do, for example:

• Free all the prisoners
  
• Open all the shortcuts
  
• Defeat The Past
  
• Try the mutations to spice the runs
  
• etc etc

With all honesty ETG is good pass your time game even for casual gamers (like myself), it might be hard and challenging at first but more runs you'll have behind you the better you'll perform. From RNG Chambers/floors to alternating bosses and weapons, every run is different and unique.
If you are a streamer, have played ETG through and would like to spice your runs a bit, ask and let your community to decide what to do in your run.
Game also has local co-op (and maybe online co-op), altho I haven't tried the coop at all so I don't have anything to say about it. 😐 But play it with or without friend(s) I bet you'll be having fun with this game... at least until you don't.

TL;DR ETG is good game, can recommend even for casual gamers and is challenging enough.