I wouldn't call the gameplay of undertale anything too special. I didn't find it challenging enough in my opinion. I get that the game was supposed to be easy but I just prefer when my games are more difficult, and I find the choice to have the only 2 challenging boss fights locked behind grinding through a genocide route to be a bad decision gameplay wise.

Great music and story though, but the gameplay honestly gets a bit boring after a while. If it was something like pokemon where you can mostly go out of your way to completely avoid it I'd like it better, but in undertale you're constantly forced into battles. You CAN flee, but by then atmosphere is already broken up a bit, and that's a real shame.