[Edi]

The thing is, you don't need to be a modder to use mods if you so prefer and even unmodded, you can get a lot of mileage out of the game. I also play mostly SP and there are a few mods (as well as map tricks) to make the AI more challenging. You can always ask for advice on that and you will get it swiftly.

LDiCesare did a good job of listing the main points of improvement, which along with the bug fixes and new content make the game much better than Dominions 2.