QBJ3 is a very ambitious mod for Quake (1996)
It has new weapons, new enemies, new powerups; and what hasn't been outright replaced has been either tweaked or at the very least reskinned to a very high quality. Community mappers then made 77 (77!) maps for the thing, all packed together into this mod. (I also made one of them!!).
As is to be expected of a community project of this size, not all the maps are good, but nearly all are at least interesting in some way and I would commend the vast majority of the ones I've played.
Along the top bar you can find in no particular order:
I loved making a map for this (its 04 on the map list, Section 28 , go play it its great), I loved playing through other people's efforts and seeing the vast amount of creativity on display. It is truly wonderful to see in a way that words cannot convey.
If you're short on time, here's a few maps that really stood out to me for various different reasons. You can match their numbers with the map of the hub on the review page to find them:
You can download the whole thing here here. Its not hard to set up, but if you're truly terrified there's also a standalone version that doesn't need a copy of the original game.