The only other Q3 mods that I can think of that you could deem large would be Bid For Power, Gundam Universe, Urban Terror, and PAD Mod.
 
Bid for Power is finished, but its animations were done via the player model and it had several people in its staff.

Gundam Universe is still in developement yet, and it's been around for a long time.  After Gen, I am most looking forward to a release and final version of this mod.

Urban Terror is not a very big mod in the traditional sense, but it's been continuously refined over the years.  And eventually, it will be ported over to Enemy Territory.  (Has it been yet?  I'm not sure.)

And then there's PAD Mod, pure gold right alongside Generations Arena.  This is a mod that I have been looking forward to for quite some time, and it's been in development almost as long as Generations Arena has (possibly more?)

Semi-Rant (More of a statement of fan-dom than anything else.)

 The only difference between PAD Mod and Generations Arena is the amount of staff each team has.  Tabun and Phoenix have worked their ass/tail feathers off on the mod.  While a two man team gets you a really cohesive-feeling game, it also makes the deadline loom far into the future.  Of which, if it weren't for the website (and the webmonkey Con,) Warden providing the hosting and laying down the groundwork for the mod, the consideration for copyright (kudos to Leemon,), the beta test team and the weekly games, and the many mappers (Reboot, Angst, and many others,)  that have made some stellar maps, yeah Gen probably would have faded  off the radar.  I seriously question whether or not that would have stopped Phoenix and Tabun though.  They're machines with an undying passion for their work.

Whether or not a modification/game is well known, sometimes, something comes along and just knocks everybody flat on their ass.  I think Generations will be the same way once everything is finished.  For right now though, I'll just keeping putting my bets on the WHS team and enjoy the unfinished ride because I've never fallen off or been disappointed yet.

Don't forget thanking Ward for hosting us Kain, and getting the coding ball rolling or we'd have no home for this website and I'd still be trying to figure out how to do a class system.

Tab:  So you're saying you had tailfeathers at some point in the past?  Ahh, your secret is out!  Now we finally have the explanation for that super-human rail of yours.  

I'll have to disappoint you there Phoenix - Human flesh and Zen meditation is the basis for my tricks. I just like to stick feathers up my ass and walk around like a turkey. Sigh, just too little time to do that these days..