I tried playing without killing anyone, cause that seemed what you were encouraged to do and it seemed the proper way to do it. But I couldn't figure out what to do with Toriel. I tried to see if something would happen if I got her HP down to low, but accidentally killed her. So I reloaded and figured out what you have to do is just stall, which is the way to do most of the big fights.
AND THE GAME KNEW I RELOADED. Somewhere there must be a secret file that saves without your knowledge. That was wild. And the saving and reloading thing turns out to be a big thing in the game world.
♥ Alphys btw.
Another thing that's cool is when you're told to input a name, that name is NOT the main character, Frisk. (I already knew that name and was going to put it in, but I was told that would complicate things so I just picked "Jack" instead. Turns out that's the first human's name and not the protagonist.
The most meaningful thing to me was during the epilouge wandering around the world, heading back to the beginning, and finding Asriel! (who again, I knew of his existance thanks to unavoidable chat and images and such online, but didn't know what his deal was.) He talked about how the first human hated humanity and had this negative attitude, which helped kick off a lot of the events of the game. (and reading about the genocide aspects of the game, is VERY villain-like!) And Asriel's new positive attitude on life after having been Flowey for so long.
I was reminded of myself. For some time, I've mused around about how much humanity pissed me off and how they angered me and disgusted me so much. With my OCD, things on the news that I see ruminate with me and I just stew. A lot of events have started to give me disgust at my species. But in a weird way, after having the conversation with Asriel and learning about the human (whose name is actually Chara) It sort of gave me a new positive outlook on life.
Now this is where I would try the genocide run but I'm really not too keen on that. Plus theymake it clear in the game that if you reset your game, you're just using the power you tried to stop, as if the correct answer is not to play the game again. (though i can cheat and just make a new profile on the Switch.)

Honestly no one is really a bad guy, except for maybe the first human Chara and his hating of humanity attitude, which drove a lot of Asriel's actions, and as I'm reading, the Chara being a villain thing becomes more apparent when you do the Genocide route and sort of awaken him with your actions.
Though really the big main villain if you do the Genocide route is the player.