Comparing it to Civ 4..

[LDiCesare]

Late game in Dom 3 can be at least as boring as in Civ 4. Make sure you set victory conditions to f.e. victory points else you'll have a boring end game chasing the last atlantian out of its last sea province.
Dom3 is very moddable. Of course, contrary to Civ 4, you can't mod everything since you don't have the source code, so people who tell you that dom3 is great because of its mods are not comparing it to civ4, as civ4 is 100% more moddable.
Civ4 can be extremely enjoyable. The Fall from Heaven II mod, where everything is remade, magic added in the game, where the world changes based on your actions (armaggeddon counter) changes the gameplay more than any dominions mod can ever hope to.
This said, I like dom3 more because there's always so much to discover in this game.