I still wonder why we can't get some kind of 'automate' commands for mages to search out sites in owned provinces, or priests to build temples, or any kind of repetative thing that will occur over several turns. I'd also like to be able to set travel destinations that require more than one turn and not have to continully tug my slow troops one province by province every friggin turn...
Little things to be sure, but get enough little things right and they make a big thing
As to best SP game... well alot depends on what you are looking for. Certain settings handicap either the player or the AI (as GP pointed out), and setting up 'themed' games, like one human race aginst all the nonhuman races (or vice versa) can be entertaining from a RP point of view. I usually don't play with Ermor active though, since the other AIs just can't seem to handle them, and if I don't start close to them to keep them in check, they tend to just overrun the rest of the map. That can be fun to play against too, but it also gets a bit repetative.