[Edi]

A game called DragonQuest, originally by SSI, later acquired by TSR and quietly buried after an abysmal 3rd edition (2nd Edition was great) would work very well for a Dominions campaign. It would require a magic system conversion and I toyed with that at one point but it was a bit much work. Kaljamaha worked a lot more on it, but I'd need to check our notes on where we got. Dominions monsters are very easy to translate from Dominions to DQ format. A lot of them are tough and scary and the various unique summons like Elemental Royalty are, in DQ, basically a free-roaming apocalypse. You either get the hell out of their way or you die.

DQ has a skill based system that in my opinion works better than anything else I've seen, though it starts to break down at the higher end of magical skills because those go so high. The system is not the easiest possible to pick up, it has a pretty steep learning curve and probably requires a couple of thoughtful readings of the basic mechanics before it starts to click.

You can find DQ on Google Groups, there are a couple of mailing lists and the actual game manuals plus a couple of user-made add-ons that I'd highly recommend.