Taking an interpretation of "unique" to include exceptionally strong in some facet, my list of unique or underrated games:
Visuals:
Haze (https://itch.io/jam/brackeys-14/rate/3850677): Highlights the impact that detailed visual flare can have above and beyond just the hitbox areas.
Tower of The Biscuit (https://itch.io/jam/brackeys-14/rate/3851771): Great visual feedback on scoring both during the build phase and at the end of each round.
Risky Fishing (https://itch.io/jam/brackeys-14/rate/3850495): Each round ends with giant fish piñata-like explosion to tally up the final score. This gets really impressive when you've just gotten through a really good run. Making loot/reward feel good makes the game feel good.
Bark Bark Biscuits (https://itch.io/jam/brackeys-14/rate/3851061): Really great scene transitions here. This makes progression feel intentional and not rushed (vs just hard-switching directly to the next scene).
*WILDLY UNDERRATED* Gorblo vs. the Haunted Critters (https://itch.io/jam/brackeys-14/rate/3846656): Really just has everything? You wouldn't even suspect this to be a game jam game if you encountered it in the wild.
Audio:
Die On The Tether (https://itch.io/jam/brackeys-14/rate/3848007): Incredibly immersive audio for looting derelict spaceships. Audio is not just music and triggered SFX, ongoing environmental sound can carry immersion a long way.
Great takes on risk:
Risk-o-matix (https://itch.io/jam/brackeys-14/rate/3848239): Pits the slow grind of loot hunting against the risk of challenging stronger enemies for quicker loot progression. The player gets to set their own pace on difficulty without getting forced into something that is too challenging or too boring. You don't need to explicitly set a difficulty in settings to make that happen.
*underrated* DEPNULL (https://itch.io/jam/brackeys-14/rate/3851617): Balance the odds of winning on a slot machine vs. the risk of breaking it. But also, you have to eventually break it in order to continue. Building systems that turn the perceived bad thing into a critical tool can lead to some very interesting dynamics.
Grapple Snacks (https://itch.io/jam/brackeys-14/rate/3850262): You grapple onto biscuits with the ultimate goal of eating them, but then you no longer have that grapple point to work with. Some forethought on sequencing is definitely required in the later levels. Takeaway is that surprisingly puzzley aspects can emerge from ostensibly non-puzzle genres.
Unique gameplay:
*underrated* Bomb or Kill (https://itch.io/jam/brackeys-14/rate/3808626): Tasteful use of AI to create a scenario that will test a completely different skillset than your used to in a videogame.
*underrated* Spinergy (https://itch.io/jam/brackeys-14/rate/3849658): You don't need a story in order to have fun building a number factory.
*underrated* Carbon (https://itch.io/jam/brackeys-14/rate/3849620): A really great exploration of a central puzzle mechanic.
Makin' Biscuits (https://itch.io/jam/brackeys-14/rate/3842227): Cute Factorio.
Cloud Top Bakery (https://itch.io/jam/brackeys-14/rate/3849626): Really creative tutorial setup. You get the rules of the game in text plus a live micro version of the game to play around with to see how everything works. I also love the title screen pixel art which does perspective outside the usual top, side, isometric trio.
*underrated* The Greatest Biscuit Heist (https://itch.io/jam/brackeys-14/rate/3852044): Hard skill-based movement, but a great example of implicit difficulty scaling. As you get closer to the prize, it is inherently more difficult to control your character due to the longer tether.
Lucky Loop (https://itch.io/jam/brackeys-14/rate/3851875): Establishes lots of different "archetypes" for roguelike upgrades and deck (wheel) construction