I wanted to play the game, but I have a pathetically weak mind towards literally anything even remotely related to horror, so the moment I got hit by Flowey's "Friendship Pellets" annd he did his signature grin I quit the game.
That said, i did watch a playthrough and I'll have to agree with people here on most things, my only real problem with the game is... (big ending spoilers here, especially towards No Mercy, you've been warned)
That said, the game is overall great and everyone in their lives should play it/watch a playthrough of at least the Neutral and Pacifist endings, (unless they can't stomach flowey, like me). Plus, awesome soundtrack, you can't ever say no to that. :V