Seeing as this is a 23 minute short for an animation project, you will forgive me if this review is on the shorter end.
Death Billiards certainly does a major part of the entire point of an animation project: It looks GREAT, with a lot of strong shots to show off not only how pretty it looks but some good use of things such as perspective and coloring. I'm not an expert in terms of graphic design so I couldn't go into great detail, but it pretty consistently looked good and used a variety of types of perspective. The sound was also solid, from the voice acting to things like the drink glasses and pool shots.
The one shot episode story could have been done better: The young guy (Otoko)'s breakdown scene where he runs around to escape and whatnot for example along with some pointless repetition of exposition, especially of the "I can't tell you anything" kind, probably should have been shuffled around and cut to make room for a bit more of the two pool players interacting or somewhat more in depth flashbacks (perhaps add a minute or two to the length?) as it makes things like the episode's climax or the later breakdown a bit less of a connection.
With only one episode's runtime worth of space there isn't much room, but I could definitely see more being done with it (This is a concept that has certainly been used in a few places, most prominently in my memory The Twilight Zone) and it is therefor no surprise this inspired an anime in Death Parade. On that note, Decim and Onna are well characterized despite being very background characters: The mysterious arbiters of this afterlife in-between, with Decim being the colder one who talks less while Onna is a bit more inquisitive (mostly in the last scene) but has the same level of empathy. It is reasonably well done.
The final verdict is Death Billiards is a good visual showcase, exactly what it was designed for, and a good watch if you plan to watch the Death Parade anime given that is where it started. A reasonably fun use of 23 minutes as well, especially if you enjoy the synopsis.