The default software synthesiser on Windows can show its limits when playing too many notes at once. Take this piece for instance, which heavily glitches at 2:07 on the large descending sweep of notes. Let's fix that, shall we?
A brief detour is unavoidable here for public safety. The piece above is not, and has no relation to John Stump's Faerie's Aire and Death Waltz, which is a piece of sheet music artistic in its own form, completely unintended to be played. In fact, it's a piano arrangement of COOL&CREATE's remix of U.N. Owen was her?, a stage theme in the Touhou Project. At least two YouTube users uploaded this piece with the completely incorrect name, causing much confusion.
Without using a different synthesiser, Synthesia plays the piece slightly better, but still glitches unlike Mac OS X or TiMidity++ on Linux. Because Synthesia separates the tracks in a file and allows you to individually enable them, I suspect that it instantiates a separate synth for each track, then has their outputs mixed afterwards, thus being less likely to hit the note limit. I don't actually know if it works this way, so take this with a grain of salt.
Installing the BASSMIDI
software synth fixed the playback issues. However the recommended soundfont,
appears to have a less clear piano sound than the Windows default
gm.dls. Rather than try to convert the latter to SoundFont 2.0 format,
I've found another that sounds better than both: Shan's Soundfont. Of course,
the improved sample quality comes at an expense: a file size over four times as
large, but it's completely worth it if you're like me and you have a large collection of MIDI music.