I actually did try Batteries Included twice on multiplayer. It would've been much more fun if there were 20 players instead of 4.
I've never seen a server that had 32 players in it. The most I ever saw is 20, and that was on Vericose Veins Guardian.
The last time I played D3 multiplayer, the levels that I usually see in play are: Skybox, VVG, BI3, Vamped, Subway and Halcyon. There were also one or two Co-op servers set up as well, probably due to me expressing my displeasure at no Co-op servers. The turnout was surprisingly good despite Co-op being bugged.