Quick post to keep the mind going... I've run a number of pseudo-historical campaigns over the years, with some good results. Here are two of the campaign settings I've used:
I used the old AD&D Historical Reference Guide for The Crusades to develop the core of this campaign, which I ran using D&D 3E. Major historical deviation was that it was set in a D&D version of Aerth rather than Earth, so there were elves, dwarves, old gods, etc. Developed quite a bit of background, drew up a bunch of maps, had some fun. The primary goal of the campaign was for the adventurers to find an ancient aegyptian treasure that had been stolen by local bandits long ago and hidden away, tied in with an ancient tomb where several of Alexander the Great's loyal followers had been buried. The group found the tomb, which was based on an old tomb from the Valley of the Kings, but we never finished that campaign, and they were left still exploring the tomb...
Another Aerth campaign, this time actually using Dangerous Journeys, set in the time of King Richard the Lionhearted in a very alternate Angland where the island was broken up into many petty kingdoms and London was a Free City. The adventurers were tied into the latest battle between the cultures and gods over the island; they eventually recovered the scabbard of Excalibur, though it was left open-ended at the end of the campaign where the scabbard would end up. It was presumed, of course, that it would go to the young Prince of Logres, from which the Brythokelltic Renaissance would start and eventually re-conquer the isle (and flow back onto the Continent to conquer the Low Countries).
As you can probably tell, I really like Gary's Aerth setting. It is my "go-to" setting for pseudo-historical campaigns.