As I mentioned in another thread, I've come up with a way to make Emperor more difficult without relying on tactics that feel cheaty. (Trading tricks that only work because the AI has stupid amounts of money)
Basically, I immediately DoW every Civ on first contact and I never accept peace treaties. That forces me to be very careful about how I play, whether I'm going to be warlike or not, and it's a much closer simulation of MP, which is what I hate about Deity. Deity is harder in *all the wrong ways*.
Sadly, the only way I've found I really enjoy Civ5 Multiplayer is Hotseat though. Simultaneous turns = different game and ultimately less fun.
(Side note: Playing this way gives *really weird* results. The AI will offer insane deals for peace treaties at seemingly random times. It's awful tempting to take a deal when they offer 1000 gold and 3 luxuries, when I'm not even attacking them or near their borders)