Warhammer online was one of my favorite MMO's back in the day. Large scale pvp battles on huge maps. Unit collision allows for the formation of actual battlefield formations and lets tanks form solid frontlines.
Unfortunately it was run to the ground by EA sharing a similar fate to many other games they eventually came to have ownership of. Thankfully, we have Return of Reckoning, which is the ONLY functioning private server and has a very healthy and active player base.
www.returnofreckoning.com/