I found a nice article on MegaWars III the other day. MWIII was the CompuServe version of the GEnie game Stellar Emperor. (MWIII came first.) The article is a good (better than my own) overview of the game.
My only nit with the article is that it refers to the games being different on the two services. I played both games during the 1986-1989 time frame and I would disagree. They were identical at that point. The author may have been confusing Stellar Emperor with Stellar Warrior on GEnie, which was a simplified, ship combat version of the game which was not available on CompuServe or he may be referring to developments in the game past the time with which I am familiar. I recall going back to GEnie in the early 1990s and finding Stellar Emperor had been changed quite a bit, but not for the better. Perhaps CompuServe kept it in a more pure form until its demise.
The article, by Maury Markowitz, is available here.
Between the two services, GEnie and CompuServe, I preferred playing on GEnie. At first the pricing was better, but later on I had built up a network of friends on GEnie, and that is a big reason I play any online game.