It's difficult to talk about how perfectly Undertale's Hopes and Dreams ties into the game's story without dipping into major spoiler territory. Luckily, this lengthy tune is capable of kindling tons of discussion based on its structure alone.
Toby Fox's retro-style RPG earned a lot of dedicated fans when it hit Steam last fall. Of course, it's earned a lot of detractors as well. Some of these naysayers are spoilsports who are down on the game's (admittedly fervent) fandom, but Undertale has plenty of room for valid criticism, too. As a spiritual successor to Shigesato Itoi's Mother series, Undertale probably won't grab you if you're not a fan of JRPG tropes that revolve around hopes, dreams, and random battles.
But I firmly believe anyone can appreciate Undertale's soundtrack. It doesn't matter if you're a die-hard JRPG fan. It doesn't matter if you think random encounters and 8-bit sprite graphics can die in a pixel-fire. It doesn't matter if you've never touched Undertale, or have no plans to. There's no reason to exclude Undertale's soundtrack from game history's grand list of great bleeps and bloops.
Toby Fox was a music composer before he was a game programmer. He produced music for Andrew Hussie's popular (and recently wrapped-up) interactive webcomic Homestuck under the What Pumpkin label. One of Undertale's most celebrated songs, Megalovania, actually features in Homestuck, though the tune was originally composed for the Earthbound Halloween Hack.
Megalovania's popularity is justifiable, and its role is certainly appropriate in Undertale (which, again, I won't highlight because it's rich with spoilers). But I feel Hopes and Dreams better showcases what Fox is capable of as a game music composer. It's all over the place, but in a thoroughly good way.
Hopes and Dreams is most notable for how it mixes orchestral instruments (albeit synthesized ones) with chiptunes. If someone who's even a little less than hyper-talented tries to make soup out of violins, electric guitars, drums, a cello, and a fistful of Game Boy chiptunes, you're going to wind up with a disaster.
Hopes and Dreams is the complete opposite of a disaster, though. It's more than final boss battle music. It's the kind of song you want accompanying you as you whip down a highway with your windows completely unrolled, perhaps doing 20 over the speed limit.
(Disclaimer: Consume responsible amounts of epic final boss music when operating a moving vehicle. Always drive safely).
Hopes and Dreams segues into Save the World (well, it does so in the music file, anyway. In-game, there's actually a long pause between Hopes and Dreams and Save the World for story-related reasons. The songs are bridged by Burn in Despair!, and everything comes to a head with the heart-wrenching His Theme). Combined, Hopes and Dreams and Save the World collect and re-master many of the themes you hear throughout your adventure, which is a perfect way to cap off your journey. You hear new takes on Your Best Friend, the aforementioned His Theme, and a much rougher, more rocking version of Undertale's gentle main song, the titular Undertale.
In fact, Hopes and Dreams is a good showcase for Fox's skills specifically because it demonstrates how good he is at turning old songs into completely new experiences. Did you realize, for instance, that Waterfall is a remix of Undyne's theme, Spear of Justice? You can be forgiven for having it slip your notice: The former is as dark and melancholy as the area it plays in, whereas the latter is as spirited and reckless as the warrior it belongs to.
If you ever have some time to yourself, go through Undertale's soundtrack on YouTube and play with each song's playback speed. You might be surprised at how many tunes share the same heritage.
And whatever else you do today, do it with determination.