I'd have to plug some of mine;
X-Worlds #06A (Forum Link + Library Slot) & CoSH (Forum + Library) ... both of which aim to alter gameplay in different degrees. Note that there are supplemental files of other assets for these too in the library.
The first makes extensive graphic, race & political & etc changes (for DA & partially for TA) and the second is more like a swift total conversion along with a Minor races package (for TA only).
Right now i'm mostly in temporary idle-mode for modding - but, if Life (as in personal issues and stuff) gets a lot better i might return later to update them with even more features (as seen in the readme files & folders in their zips).
Mods are kinda tricky and it's "difficult" for anybody to suit everyone's hope for whatever they want or need... XW is in fact a clear immersion attempt into the Mythos X-Com franchise (including Apocalypse) and who really doesn't know Super-Heroes with CoSH. Understand also that such mods take HUGE amount of time & resources to make. Just the ships & fleets for the XW 39 races has proven to be quite challenging & complex, for example.
Essentially, *You* have to try out anything just to get an idea.
I'd say that each & every uploaded mods have their potential, some are obvious while others offer much more than simple features.
