Best Game I'd Ever Return
It's kind of impossible to talk about Undertale without acknowledging what it does differently; there isn't a game out there that has a battle system quite like this one. Unless you "play the game wrong," it plays almost like a visual novel by selecting actions and seeing how the monster responds before smash cutting to inventive bullet hell-like segments. All this with the sole motivation not of killing, but of making friends. It is, after all, the game where you don't have to kill anyone.
Some late-game bosses, especially the only two challenges on a "No Mercy" route, make it explicitly clear that a unique battle system doesn't necessarily mean good. The appeal of Touhou-style shooters is already debatable, but ones with a wonky hitbox where your icon doesn't move quite as quickly as you want to are kind of objectively bad. It may seem like a minor thing, but the basic action of moving from Point A to Point B majorly impacts how much one enjoys a game. For an example of this, compare Super Mario 64 with Bubsy 3D. While they both exist in 3D worlds and are platformers, in one of them you can walk forward, jump where you want to, and seamlessly change directions. The other is Bubsy 3D. There are several reasons why Bubsy 3D has been lampooned, the difficulty in movement is definitely part of it.
Even then, the appeal of the Touhou series, and other top-down modern top-down shooters, is finding the precise spot where you can avoid the boss's waves of bullets. You move at an exact pace and just as fast as you need to. Even the new bosses in Binding of Isaac: Rebirth did this properly. Unfortunately, it isn't quite up to snuff in Undertale, where it rarely feels like you're at fault for getting struck by an opponent's attacks. More often, it seems like you just haven't memorized the particular monster's attack patterns. The times the attacks reflect the events of the battle are cute but ultimately hollow.
Making friends with the monsters appears to be a peaceful way of ending conflict, but if one simply thinks of the various commands, like "Flirt" or "Joke" being different attacks that beat each enemy in three or four moves, it starts feeling like a conventional RPG wearing different clothing. It's left as a fairly typical turn-based RPG with a watered down shoot-em-up as the main gameplay component. I'd agree it hasn't been done before, but maybe for a good reason. Except for two fights in particular, it's never hard, but always either frustrating or just boring.
There are elements of games other than the mechanical interaction with the game world, of course. It's difficult to discuss those without spoiling large parts of the game's plot, which I'll try to avoid doing but is likely inevitable.
Thematically, the game is kind of a mess. I won't call it a gimmick, because that's too damning of a word, and I won't call it a quirk, because that's just too insignificant. Somewhere in between those two, however, is the fact that you don't have to kill anyone or anything. In fact, the game actively punishes you for doing so--character interactions are limited, if not outright removed, less options are available, the game breaks the fourth wall and admonishes you, the player, for your barbaric and murderous actions--preventing you from the "True Pacifist" ending which answers all questions you may have had about the game.
A significant part of getting this "True Pacifist" ending involves "dates" with the characters you've met and befriended throughout your journey. Setting aside the implications of your character implied to be a child and the characters you date implied to be an adult, the final date involves forgiving a lizard scientist for doing a whole bunch of things wrong. Credit where credit is due, the game doesn't try to hide that she's really messed up and hurt a lot of people because of her own selfishness. And yet, you forgive her. The final boss of the "True Pacifist" run, the main antagonist of the 6-8 hour game, is forgiven as well. Because that's what the game is about; unconditional forgiveness.
The one exception to this central theme is yourself, apparently. If you treat Undertale like a normal game and ruthlessly murder every single monster in your path (as you may begin accidentally), because, as you've been taught to or because of your own curiosity, you can never ever get the "True Pacifist" ending again. Even if you just accidentally kill an enemy (for reasons covered in a bit), you're locked out of the True Ending for that run, and the game will remind you of that later on. For a game that's all about unconditional forgiveness, it certainly holds every single mistake over your head.
Your whole drive to participate in the game's pacifistic side lies in the cast of characters you'll meet, ranging from a pair of skeletons with a dynamic like the Japanese manzai style of stupid-and-smart comedy to the conflicted yet determined goat king of the world of monsters. The characters are developed and are clear in what role they fill in the story, from their dialogue to design. In the fights against them, it's clear what their personality is and who they are. There's a good sense of character in the monsters, which makes it even more of a shame that they feel like the manifestation of rejected Adventure Time punchlines.
With few exceptions, you'll find the main cast either endearing or aggravating--if you're sold by their introductions, then you're sold on them, because only the previously mentioned dinosaur scientist and the main antagonist are ever fleshed out in any way. The rest of them act predictably, reacting to new situations in exactly the way you'd expect. There's consistency, and then there's predictability.
The game's graphical presentation isn't great, but since information is never confused and you always know what's going on, it gets by. Considering the main guy behind the project was previously best known as the guy that did approximately half of the music for the popular webcomic Homestuck, I wish the soundtrack had been a bit better. The music loops rather repetitively in almost every scenario, and so much of it are chiptunes that I'm left wishing that the moments they weren't were more frequent. I know that the particular musical choices were made to reflect the turn-based RPGs that Undertale takes inspiration from, but that always felt like a choice made from necessity. If a game can have more variation in the tracks heard, like in Earthbound, then it's an opportunity well worth the effort. It doesn't knock points off, but is greatly appreciated and curiously absent.
There are a few tracks that stand out from the rest, and have captured my attention as part of the best segments in Undertale; the final bosses. I'm fully honestly when I say the final boss of the "Neutral" and "True Pacifist" runs are among the best experience's I've had with games in 2015, and up there with The Wonderful 101 for best final boss, period. It's a shame, then, that the final boss of the "No Mercy" run exhibits the worst problems of the battle system. It's supposed to be frustrating and difficult, yes, but there's a much better and satisfying way to do that ball-crunching difficulty. Even the battles I enjoy, which are enjoyable mostly because Undertale stops pretending it's best as something like a visual novel, are host to their own problems.
There's also an issue with communication to the player. Early on you meet a frog who tells you that, if a monster isn't being agreeable (read: if you can't go through the proper channels to be merciful,) you should soften them up a bit to grease the cogs a bit. Right after this is a fight where you must do the same action more than twice with no change in response. If the second time you get the same response and, understandably, think you're at a standstill, you might take the frog's advice and fight a bit. Try to get the health down a bit so you can reason with the monster. When monsters get to low health, however, you suddenly deal way more damage, leading to you accidentally killing someone you honestly didn't mean to, all because you took a frog's advice. There's a boss later on that, in order to advance, requires you to run. Every single instinct playing games has taught not only to never run away, but that bosses are the one enemy you can't run from. But for this one battle, with no prompting, that's what you must do if you hope to keep with pacifism or not die. Those are but the most major expressions of poor conveyance, with the most minor being guessing which action to take to please a monster into giving up the fight.
There are some other things that rub me the wrong way about Undertale, like the poorly paced meta-narrative that I'm usually a huge fan of, the excessively long lava world, or the music that feels as manipulative as the four chords used in seemingly every Top 40 hit. Some things I really did enjoy, and think will stay with me as some important lessons on game design and what I find enjoyable. The problem is getting to the nougat center of Undertale involves slogging through 10 feet of a sloppy, almost calculated to control your emotions, chalky garbage chocolate.