[alexti]

Dominions is somewhat unique in its SP gameplay. I'm aware of at least different styles:
1) Purely strategy game - you play to beat AI in the most efficient way. This has somewhat limited longevity (maybe few month, maybe a year, depending how quickly you learn). At some point you'll become proficient enough that even impossible AI won't be a challenge;
2) RPG-style - the game has a lot of atmosphere and you can play "thematically" instead of using optimal strategy. It often leads to unusual games with interesting situations and challenges. In this style the game will play different for almost every nation and it will have huge replay value.
3) Experimental strategy style - in this style you play various interesting strategies (in efficient manner). The difference from (1) is that you intentionally don't play the strategy optimal AI, but choose some other strategy (probably promising against another human player) and try to play it against AI. This is also pretty much unlimited in terms of gameplay.

(1) is usually grows into MP and (3) probably often co-exist with MP.