What I think of as my “home server” in Team Fortress 2 runs just one map (2fort) with increased teams (16 per side) and a long running time (up to 3 hours). I found this very helpful for learning the game, as I did not need to simultaneously learn a couple dozen maps (including stages), nine classes, alternate weapons, etc. One map, enough people for my beginning incompetence not to doom us, and time enough to settle in and explore without frantic NOW rounds.
I moved to that server after starting to learn on a 2fort server with instant respawn. Instant respawn is nice for a beginner who dies a lot but utterly unsuitable for a real game on many maps, especially 2fort. If it takes longer to reload than to respawn and get back to the fight, the game is an extended stalemate. Maybe one side will eventually get a lucky grab or a really good spawn-camp going.
I am coming to see increased team size as a similar problem. Rounds still end, because many shy from playing defense even as the intel is running out the door, but large teams mean that there is always more defense available. Killing one per second is barely keeping up with the respawn. Furthermore, that defense is always there, even while mounting a big attack. You can have 3 Engineers, 3 Snipers, a Demoman with stickies, and a Pyro spy-checking at all times, and half your team is still available to assault your similarly staffed enemy. If your assault is going well, the (entire) other team respawns behind you, while any replacement attackers are 10-20 seconds away across prime Sniper territory.
Hence the 3-hour running time. Unbalanced teams can sometimes end it early with a string of wins, but it is not uncommon to see time reach 00:00:00 with one win and a cap or two into a second round.
I have been enjoying an Arena server on the side. “No respawn” solves many problems.