Install the Ultimate Quake II Patch to restore the Sonic Mayhem soundtrack.
As for the gameplay, it's alright for a 90s PC expansion made by a different developer. The new weapons are a lot of fun to use, but the last few stages can become really tedious having to wittle away at numerous beta class gladiators around every corner that have energy shields and beefed up health. It's not a problem if you're speedrunning, I guess, but in my opinion they tend to slow normal gameplay down because there are so many of these punching bags to go through near the end of the game; not hard, but somewhat boring. The standard Strogg guards are now equipped with hyperblasters, ion rippers, and Warhammer 40k style red laser flashlights that are suprisingly accurate and damaging, unlike the Imperial Guardsman's lasgun. The railgun or rocket launcher makes quick work of them at long range when you get it, though.
TL;DR 7/10, it's alright, worth playing at least once