I am a long-time DR fan who played this game at is original ENG release in 2015. I am telling you, Two Stars is Extremely Generous.
Gameplay-wise, UDG plays very similarly to Portal. Not nearly as good or well-executed as Portal. But Portal, none-the-less. You have a gun-adjacent item which I will Call A Gun Anyways, the gun switches between fuctions, you avoid or kill enemies by screwing around with the Gun and/or other enviromental items in the area. Or you press the cheat button and rip through as Syo if you only care about the story.
I can't see why you would care about the story, however. Barring the fact that "this is Dangan Ronpa, a franchise that NEVER should have had a 'localization', it should have had a pure translation with heavy tranlators notes for context, if it ever even should have come West *at all*"; UDG does exactly what it set out to do: End the series. Both story-wise, and in fandom. After this game, historically, was released an anime that retconned canon and threw an entire (previously canon) text-based entry completely into the trash, and one game that was made specifically as a middle finger to any member of the old fandom who wasn't completely disgusted with the heavy-handed offenses to anyone who retains their personal moral compass when engaging with ficton that are contained in UDG. Every character in DR always has been and always will be a stereotype. There is a reason the franchise was enjoyed, primarily, by ex-homestucks, a series based on numbers, patterns, and stereotypes.
The only reason I have given it an extra star is because sometimes I look at Taichi Fujisaki and decide "Yeah, I *can* live to see another day!"
If you arent offended by (weirdly realistic?) scenes of childhood assualt, enjoy area-based puzzles, early 2010s internet stereotypes, and watching anyone you love die a firey horrible death: yeah, sure. play the game, i guess. If not just.. turn off your computer and enjoy your life outside of knowing this is a thing that exists.