What I liked:
I appreciate the story that was offered to me, especially you're willing to look further than the general base. Without going to deep into it, the backstory is very compelling and can really hit you in the right areas, for example: the moments with Asriel and the fallen human. Adding to that, is the writing. Undertale can get lighthearted and humorous, while at the same time, and be grim and depressing in just the right areas. The characters, while not the deepest I've seen, are very interesting and all stick out from one another in all the right areas. Undyne is probably my favorite in this case since she has a strong hatred for Frisk early on, grows to be a be a lot more friendly with them. She also has that badass personality while being funny in the best ways. The phone calls you can have with her and Papyrus reflect this quite well. Seriously, look them up, or play the game for the different kinds of calls you can get with them. While the graphics are simple, they are effective with showing what happens on the screen and all that. If anything, I think they're clever and the simplicity works in its favor. The boss battle with Omega/Photoshop Flowey is a good example of catching you off guard and what simple graphics can do if you have a trick up your sleeve. In terms of gameplay, it's not the most exciting, but for an RPG, I personally found it pretty cool and unique with the bullet-hell style dodging mechanic. It also really added to the fact that Toby wanted each monster to be unique. The puzzles in the overworld are also pretty neat to. It gives me another reason to have some fun with the NPCs with some interesting solutions. Another thing that I enjoyed about battles is the morality system where you can spare monsters by getting to know them, which may not be the most unique thing I've seen in an RPG, it really shows that your actions are your own doing. The soundtrack is also a major plus for me. The soundtrack fits with the environment and all just great to listen to. While some tracks share similar leitmotifs, the soundtrack is so good that I don't really care that much (if the soundtrack wasn't good, it would be a different story). I'd say my favorites are Bergertruckung + ASGORE, Battle Against A True Hero, and Hopes and Dreams. The themes of a lot of the boss fights. Speaking of which, I'd have to say those are my favorite parts of the game for me. It combines pretty much everything that I just mentioned, story, character personalities, gameplay, and soundtrack, and rolls it into one neat package. A good number of the boss fights change up the mechanic of the bullet hell to something new for a brief moment, and it doesn't feel forced. Hell, I can argue the boss fights alone would pretty much sell this game. And I think the True Pacifist Route is probably the best way to experience this since the game loves to remind you that mercy is the better option than fighting. And I can agree there. Sparing monsters is the way to go, not just because it's the right thing to do, but because it's the most interesting thing to do. You get your goofy encounters, some heart touching moments, and even learn about its meta as hell writing. Actually, I can also argue that this game as a whole is smarter than gamers. It knows what gamers do in RPGs and games in general, its fourth wall breaks make this game way to self-aware, and it reflects the choices you've made and treats you on how you have played in general. Undertale is one of the most confident games I've played in a long time. Though that being said, I can't help but feel, it's too confident in itself.
What I disliked:
*sigh* Okay, all that praise I mentioned about its morality system best applies in a Pacifist Route. On the other hand, there's the Genocide Route, which is the worst part about Undertale for me, and Sans could not have said it better himself. "You're gonna have a bad time." I know that phrase is overused, but he's right, both in story and gameplay. The Genocide Route is as boring as watching paint dry. About 70% of that is just pacing in areas, grinding your way encounter after encounter until there's nothing left. While Undertale gets dark and surreal with any route you choose in general, the Genocide Route isn't surreal nor intimidating. As you go along the game with a set amount of enemies to kill, it also lowers your encounter rate which makes it even more of a drag to continue with the route. The fight command doesn't help in the slightest. All you really do is just time your button press to inflict as much damage as possible and that's it. While it is an alternative to the act command where you can purposefully do little damage and then spare, Ala Pokemon, but that's what the act command was there to do in the first place. Have a greater chance to spare the enemy without accidentally killing anyone. So, there's really no reason to use the fight command for the Pacifist Route at all. But really, the grind isn't the only issue for me. It's the fact you don't have as many interesting encounters as you do inside Pacifist and even the Neutral Route, next to no puzzles and story whatsoever. And before anyone tells me. I know that's the point of it all. I know that it was put in as to make fun of forced grinding in RPGs, I know that it's to make the atmosphere feel unsettling and sad as hell, and I know it's to make you feel like a psychopath for killing everyone you know and love. The other 30% of the route is about its dark writing and boss fights, with the latter being the only thing I found remotely interesting about the Genocide Route. So, I think the biggest problem with the route is that it sacrifices immersive gameplay to try and send a message. You are still making a game, one that people would want to go back to and escape from the real world, but pacing in circles and using the bare and bland fight command makes me want to play something else. The game is pretty good at making me feel like a psycho with hammering how much of a jerk you are for killing everybody repeatedly, which is fine as it is the message, but the consequences after the grind and difficult boss fights? Well...
What I am indifferent about:
Okay, so what does happen when you go through with a Genocide Route? You end up destroying the world. Bad news is that your game is now just a black screen with wind howling. Good news is that if you wait long enough, you'll get an opportunity to reset the game. What's the catch? It doesn't reset everything. Meaning any future runs will remind you of the mass murder you've committed in the Genocide Run and taints your copy of Undertale, forever. And yes. It's not really that permanent as you can alter the game files on your computer and delete the game memory to clean your copy, and I'm not afraid to admit that I did that as soon as I found out what happens afterward. I know I said the game is best experienced blind, but corrupting my game? Uh-uh. I know I'm responsible for my actions, but I ain't gonna let computer files screw my game over. I can mess around with files too, game. That being said, I put this in my neutral thoughts as I want to love and Hate the save file memory mechanic. I want to love it since it's a clever way of remembering the choices you've made and the actions you've caused. I also want to hate it for how its used since it take things a little too far from the already empty and boring Genocide Route. And yes. I'm not afraid I would love to see this mechanic in another game which makes clever uses, but not quite as severe as Undertale... if that makes sense. And lastly, while the neutral route has 25 endings, Undertale is kinda hard to replay going down the same path and experimenting with different ways to play since playing blind means you have to go through the same sets of dialogue over and over again just to see a different piece of dialogue Sans calls you about. I do see myself coming back for repeat playthroughs, but for a couple lines of dialogue? Eh, I can wait.
So overall, I can safely say I enjoyed this game. While the Genocide Route may be the only stain for sacrificing gameplay over sending a message, it can be ignored and you still get a game with a compelling story, fun and interesting characters, neat puzzles, clever writing, and some good gameplay. I would so not call this the "greatest game of all time" (there really isn't one to me) But I can say it's one of the best games I've played in a long time. It's not afraid of what it is and is still great experience. I bet a lot of you are willing to disagree with that I've said, but hey let's be civil here. The game is about showing mercy, after all. ;) In case you are still unsure of playing the game or not, give it a try (even though at this point, it's probably to late to get the best experience overall if you read all of this). In fact, I recommend watching Somecallmejohnny's review, (https://youtu.be/Arh0mzaQhSE?t=3m12s) I pretty much agree with him in almost every aspect.