For my part, i would never play something else than marathon. And always huge map, since a normal size map on marathon make it too easy to win by domination. And about the difficulty, i now found that emperor is perfect for me.
As you would expect, it also make a game last very very long.. you simply cannot begin a game after dinner, expecting to finish it before bedtime.. unless you want to go to sleep as the sun rises.
So, why marathon ?
Primo, as someone else said earlier, units doesnt go obselete by the time you cross the border, which is a very good thing.
Secondo, Building something take VERY long, as well as technology. You now must think twice before choosing what to build/research. You also always must be prepared for war. If you got DoW, you're left with the units you have to defend yourself.. unless you got load of cash to buy some units quickly. As well as researsh, it take so much turns to complete, that you realy need to think about what you realy want to do.
Now lets talk about cash.. everything you buy in cities cost way more. But, since there's more turn in the game, it's pretty well balanced
Now, Since everything takes longer, but with the movement speed staying the same, you're no longer in a hurry when you're on offensive. Take your time to position your units on the battlefront. If it have to take you 10 turns to take a city instead of 4 turns, at the reward of less damage on your forces, do it.. you have time.. to take your time.
So my general tips about marathon..
- Always think twice about what you build/research
- Units in normal speed are NOT expendable.. this is twice the truth in marathon.
- Take your time to position your units in a perfect combat position. Even if you lose 4 turns at the end.
- Be prepared for a DoW. Even if you're on a defense strategy, you need a strong military. If you're weak, when you got DoW, you will NOT have time to build reinforcement before half of your empire passes into ennemy hands.
- Keeping lots of cash into your vault is a very good thing. If you got DoW by someone stronger that you, it will help buy instant reinforcement. Units cost way more than in normal speed though, so you may want to have much gold to spend. Even if your GPT is gooing very well, remember the high units buy cost.. If your coffers are empty, but still make 200gpt, if you got DoW, it can take many turns for you to get enough to buy units. (without wonder or SP bonus, units in the range of infantry cost about 2000g.. so think about saving the precious cash for those momment of needs)
I hope those tips will help
Have fun in marathon !!
Sal