Don't let the memes or the cringy fanbase keep you away from this game. At an incredibly low price point, you will get an experience like none other from this game. I completed it years ago and I still think about it to this day. This is a game that will challenge you and tell you a great story with incredibly well-written characters. It will take you on an emotional journey as it contains themes of empathy, forgiveness, parenthood, siblinghood, friendship, acceptance, and DETERMINATION. No other game has emotionally hit me as hard as this one. If you let yourself get sucked in, I'm sure this game will teach you something about yourself.
Gameplay is fantastic, too. The unique battle system is a combination between the classic RPG turn-based formula and bullet-hell. And just when you think you have seen it all, this game will manage to throw suriprises at you (in a very good way)!
I'd say it's suitable for all ages, and will speak to everyone in a different way. I would say that the Genocide ending is best left to a more mature audience though (as it gets extremely dark and disturbing, and MUCH more challenging). But that ending is hard to get, as it requires killing literally everything in the game until there is nothing left (which is something I don't expect younger players to figure out unless they look it up or know about the game already).
I will always recommend this game. Just play it.

This is currently my favorite game of all time, so making this review was an inevitability, but I found it hard to word myself for the longest time. This entire review will most definitely contain elements of spoilers.

I would I guess, like to preface that it isn't perfect. Much of the known Genocide Route and Pacifist Route is a rough draft in terms of narrative design, pacing is kind of thrown to the road in both of them in terms of how events are revealed, specifically the tapes in the True Lab come to mind, or how it unceremoniously saves all of the genuine good storytelling in Genocide to the latter bits.

It's also quite limiting on a gameplay front, to an extent. I think the bullet hell combat is genuinely good, and by nature of how it's designed, better than most other rpgs. Dancing between bullet patterns as they combine on top of other enemies is a core part of any decent bullet hell philosophy, and seamlessly tying that to its rpg core and narrative is something to be praised and serves far more an execution test than most rpg's knowledge test design where ultimately optimal strategy is a once and done affair for most encounters. It is still limiting however, since only about 1/3 of the encounters actually make use of patterns building atop of each other, and the game saves its strongest bullet hell tests to the Genocide run, and the hard mode is literally an intentional joke.

That being said, and god that last paragraph wasn't even too negative, I'd say UNDERTALE is absolutely brilliant. It's the finest execution of the ensuing theme of "determination" I've ever seen in a work of art, surpassing general examples like Gurren Lagann by supplying its theme at an individual character level and wrapping it around an excellent metanarrative to boot (that you don't even have to be aware of to enjoy).

UNDERTALE works off clear character ideas, humanizing its characters around the world it sets up in extremely well written ways. Alphys is my leading example, which is weird that it's people's least favorite. She's built up as a stingy incredibly annoying type, a character who is increasingly irritating to deal with. She stops you at every point, wanting attention, to be something like the shows and remnants of otaku cultures she was able to consume. She ultimately gets betrayed by her own work, and ends up pushing back her own war crimes she's committed. She's not a justified person in what she's done, but she is sympathetic to understand. Her actions are communicated exceptionally for people to understand what kind of person she is, and the arc she gets is fitting and she learns what it really means to be determined and what she actually needs to do to be loved.

This reflects on every character not just her, and on top of this, is how flawed each of these characters are as people really works back to how honest they truly feel, and they’re all fleshed out personality wise to a point where tobyfox can publish them talking about whatever topic and I could hear their fonts come off the page and imagine them emoting in real time. They're very humanized people.

I'd also like to talk about how UNDERTALE ties its metanarrative elements well. The game in short, is a living breathing game world that operates on world mechanics riffed from a general audience understanding of how rpgs work, using a morality system that is defined on a character to character level rather than strict moral good/bad. You're allowed to kill in self defense, you're encouraged to be pacifist but the game doesn't vilify you for kills, it asks you to reflect on them. The monsters' world is as much a world to them as your own world is to you. And the only basis to understand them is to take them as living people where act of murder or self defense is a last resort. Especially when you yourself have the power to save and reload, so death is never truly an end for you, so death until you SPARE them is a legitimate option that only costs you time.

Even if you don't care for the meta elements, even if the characters aren't someone you jive with, even if the gameplay isn't particularly your own thing, it still has its own comedic writing to back on, and one of the best vidya soundtracks I've had the pleasure to listen to. It's also an excellently paced journey, gameplay and narrative-wise. But I would still be surprised personally, if there wasn't a single character or emotional moment that resonated with you.

I think UNDERTALE stands above all other games I've played in my lifetime so far, and it certainly has had a huge impact on my life going forward that I can't give it any less than my 10/10.

A really solid short game that somehow made turn based gameplay interesting with the bullet dodging stuff.

Story is great and switches from comedy to horror pretty well. All the characters are great with the exception of dr alphys which somehow is a nervous anime girl while also a mad scientist and we're supposed to just forgive her crimes against nature. Also they shoved the much more interesting mettaton to the side for her so that's a big disappointment.

Other than that though pretty great game, also very short which is probably a decent reason why it got so popular. Definite highlights are boss fights and visiting Undyne's house.

9/10

Undertale pummels the entire emotional spectrum and features the most authentic and compelling implementation of "character morality" so far in gaming history. The humor isn't for everyone, but humor never is. The soundtrack is almost unrivaled, and the battle system is both genuinely innovative and inspirationally fun. Undertale is the perfect length, with no unnecessary fat on its bones. I can't come up with any valid criticism to make this game a better experience, and it's overwhelmingly obvious that Toby Fox poured every drop of his heart into it. I'm as interested in Deltarune as the next guy, but I'm so satisfied with Undertale that if it never materializes I'll be just fine. Thank you, Toby.