Sounds intriguing. I never got into Civ 4, bought it for my father, who didn't like it (he still plays Civ3). I didn't like the graphics, but I didn't play it that much, though. I was gonna load it on my current computer, but he lost one of the discs.
I'm not sure Civ3 can be topped. It had a few good and bad quirks.
Limited horses seems silly. Resources could be exhausted in civ 3, so it's not new. Horses never were, though, because they can be raised.
Stacking was somewhat acceptable in past games because of the scale of the world, there should've been a limit though. 2 or 3 Infantry units occupying a space is one thing...30 is something else.