For an anime special, I was impressed with this one. This is a "what if" epilogue to the Angel Beats anime. If you haven't seen that, then do that first, as this won't make sense otherwise.
The art quality is pretty good, easily matching the main series. The sound direction was good as well, though nothing outstanding.
For someone who has seen the series, the plot was interesting, and even a little emotional. The new character didn't have time to be fleshed out, but the returning character got enough development in the 2 minutes there was.
If you've seen the show and enjoyed it, do yourself a favor and watch this.