I really enjoy the diversity that Civ BTS offers in terms of game length. If I feel like playing a quick game, boom, I can play a tiny map with a few civs on quick speed. If however, I want to play a full on game with my special modifications and have a real-world experience I can do a huge map, with multiple civs, on marathon speed.
Just to let you know, a buddy of mine has been working on a MOD that allows you to choose how long an era lasts, and modifies the tech costs accordingly. It's a very cool MOD, and I think if you're a marathon player you would enjoy alot of the advancements made for BTS. You can find the MOD in the creation and customization forum under "World Piece."