Is it worth it?

[AniJan]

Should I buy Undertale alone, or should I buy Undertale WITH the soundtrack?

[Dash Lambda]

The soundtrack is great, but it's all over YouTube and SoundCloud and whatnot. If you want to support the developer, go ahead, but if you just want to listen to the music, you don't need to spend money.

[Charger]

If you like sound tracks buy it with it. 

[Gale]

Just the game for now. If you find yourself liking the game towards the middle/end, consider supporting the creator by buying the soundtrack.

[TetraSky]

Just get the game by itself.

If you wish to support the dev some more afterward, buy the soundtrack. But really, there's only like 2 or 3 songs that are worth listening to outside of the game and you can easily find them on Youtube. Personally, I feel like the fan made songs made from the game's soundtrack are a lot better. Like the "Undertale Musical" from "Man on the Internet"(HEAVY IN SPOILERS, don't watch unless you've finished the True Pacifist route at the very least)

[AniJan]

Nah, I mean the dialogue.