[Taqwus]

Scenario-based games frequently pose more of a single-player challenge, as (a) the author frequently has the tools to write a customized plan for the AI, and (b) single-player scenarios tend to be grossly unbalanced in terms of advantages granted to the AI(s) to the point that were the computer replaced by even a novice human opponent, defeat would be all but automatic. In addition, the human player frequently needs to fight the interface itself and (relevant in RTSes) the fact that his units tend to be utter imbeciles who need excruciatingly exact, explicit instructions every step of the way forces micromanagement.

Random-map TBS games have a harder time giving a good game to the single-player -- the player might actually have the time per turn (if not necessarily the motivation...) to micromanage, and random setups prevent exact scripting.

That said, some more configurable games have done somewhat decently without massive scenario-specific scripting. The tactical AI of the Combat Mission series, for instance, does at least try to avoid some large possible errors (such as firing too early and accomplishing nothing but revealing one's location, or sending units piecemeal) and employs some reasonably healthy habits (like sometimes towing a gun away after its location is known, so that it's gone before your artillery responds). It may even be capable of blocking your LOS with smoke rounds, IIRC. It's not a match for an experienced human player, particularly on offense, but it tends not to make one scream at its idiocy quite as much as does, say, an AoK AI which cheerfully stays put on its tiny island and waits until the Imperial Age to build a dock. I once played a random map AoK game in which one AI somehow managed to mine *zero* gold during the entire game -- and this was a game in which I'd taken a absurd (and were it multiplayer, surely a guaranteed-losing...) amount of time building economy and teching up before bothering to assemble an attack force. How? Heck if I know...