It's UT. Very good. Chaos UT came with the GOTY edition when it first came out, but isn't here. The missing parts can be downloaded elsewhere, but it is a small faff to do so. Apart from that it is the same old game, and has aged remarkably well. Tense, frantic, fast gameplay that make the graphics from 20 years ago irrelevant
If you played Quake II in the past and want to get it back again, I would recommend this package. It is the original game, the mission packs, and EraserBot (the multiplayer bot package). Nice touch for me was having it packaged together so that launching EraserBot was relatively idiot-proof. Still need to google the bot commands though. The music may or may not work straight off, which is not ideal. There are some .ogg files in /QuakeII/music that may need CTRL+C, CTRL+V into /QuakeII/baseq2/music in order to work. Or it may be that you need to download those .ogg files and put them there yourself. It is very google-able and simple, even for someone like me. I can't remember exactly whether those .ogg files were part of the install but just in the wrong folder or whether they were missing altogether. The second thing that can improve the game is fullscreen and higher resolution, from the Quake 3.24 patch by Knightmare. Also not difficult to google and install.
The game is excellent. Top, top drawer cyberpunk themed game with options to take various approaches and decisions. This GOG version contains the GOTY edition, which does run on my Windows 11 machine, and also the Revision mod with updated textures and high resolution compatibility. The GOTY edition is fine except that it keeps cutting off the final 1 or 2 seconds of dialog in the conversations. That gets very annoying, particularly when the characters are each speaking every few seconds - you miss most of it. I have looked at suggestions online and they seem to mostly be patches or fiddles with the ini file (which did nothing to help me). The Revision mod looks like the answer. It is included in this GOG release, and has graphical improvements as well. It might not be "pure", which was probably my preference, but it is a good way to enjoy a slightly updated version of the old classic. I don't expect the differences from the original to be too significant. The only bummer is that is doesn't seem to be able to do cloud saves with Revision, only with GOTY.