The quality of a video game is subjective opinion. If you want to say what you think about how good/bad or whatever Undertale or certain aspects of it were, feel free, but stating these things as objective facts is where it goes from fair to immature. I love Undertale and it remains my favorite game of all time, but I wholly respect the opinion of others and understand why some don't like it. Guess what, not every game is for every one, and there are especially some games that are really for specific kinds of people, and the truth is that Undertale is one of them. It's a character and story driven game, which may turn away a lot of people, among other things. The important thing when handling subjective opinions is to just not be a prick about it.
The tone of your message, and the fact that you posted it in the Undertale discussion thread, comes off as pretty spiteful to me. Kind of weird to be that way over an almost 8 year old game with a much smaller fanbase than it once had.