I haven't played it in some time, but I do love the game. I've got some great memories of it. I ran two long-term campaigns using the Alternity rules before we switched over to 3e/d20 for pretty much everything.
The first Alternity game I ran was set in a highly-modified version of the StarCraft universe (from the computer game). The PCs worked for the FreeSpace Alliance, the group of Terrans and Protoss that were joined up at the end of the first game. They were in a region of space known as the Pirate Rim, which was much like the Verge from Star*Drive, though it wasn't nearly as remote. Basically, it was this big area that had been forgotten about during the three-way war on the other side of relevant space. I ran them through at least two adventures that I recall - The Last Warhulk (which I made a Creator weapon against the Zerg), and either Black Starfall or Red Starrise - I don't remember which was which. Regardless, they did the one that takes place on the space station, where you're trying to prevent the spread of the virus. Anyway, for the most part, they were working against the khep - one of the alien species I added to the setting. The khep were amphibious gangsters - somewhere between the Hutt from Star Wars and the D&D aboleth. They were big into genetic engineering, and over the course of the campaign, it was discovered that they were so good at it mostly because they had been studying the Zerg for longer than most people had known they existed.
Let's see here. Trying to remember the races I had for that campaign. There were the Terrans, humans who had been sent to this region of space as castaways several hundred years beforehand. The Protoss, who were powerful psionicists, and very high-tech, most of it based around their affinity for psionics and their strong links to the region's dominant Creator race. The t'sa, the small lizard-people from the Alternity PHB, were a small independent race that sided mostly with the FreeSpace Alliance, and served mostly as techs and engineers. I kept their culture largely as it was in the books. The Aleerins (calling them a mechalus was insulting) were also much as they were in the APHB; they kept themselves as seperate as possible from the conflicts all around them, mostly dealing with internal cykotek problems within the race. I used quite a bit of Egyptian flavor for them; I thought it made the race more interesting. The khep (who I've already described) kept two slave races. The weren were similar to what's described, but I put some detail into their culture. They were still very warrior-oriented; I mixed the Clans from Battletech and Klingons for their flavor. They were actively fighting against the yoke of khep enslavement, which was one of the major subplots of the game. The hanille were basically sesheyans who looked different; they were arboreal monkey-kobold-flying squirrel things, rather than the creepy jungle gargoyles that were the sesheyans. There were a few AI and robot characters that the PCs met, as well, though no one expressed interest in playing one.
But enough about that campaign. I can post more, or dig up the web page I had for it, if anyone's interested.
The other Alternity campaign I ran was known as Agents of the Crown. Take Colonial America, circa the 1760s. Add equal dashes of DarkMatter, X-Files, and Call of Cthulhu, and you're there. The PCs worked for the British Crown, as agents for a soceity devoted to protecting people from the supernatural. Characters included Silent Hawk (an Indian shaman), Dwight Baston (a failed doctor who became an investigator and student of the occult), Uriel (an angel who was sent to Earth because he interfered too much with humanity), Siegfried van Richten (an Enochian - a student of white magic), and a Catholic knight whose name I do not recall. The best adventure we had was an old one from Dungeon Magazine that I adapted. I don't remember the name, but it was a Ravenloft adventure that used the Doppleganger Plant, aka the Invasion of the Body Snatchers. Paranoia, backstabbing, and carnage ran rampant for about four sessions as they went through that.
The main plot for the campaign was that a sect of evil druids - the Shadow Circle - were trying to ressurect/reawaken a spirit of destruction called The Morrigan. They were in cahoots with a group of vampire necromancers, as well as an independent operative named Pierre le'Fonnet (the nemesis of one of the PCs). Unfortunately, the game ended before that plot could come to fruition.
Though we're not using Alternity for it this time, we did recently resurrect that campaign. When my online D&D campaign came to a close after two years, the players convinced me to start that game again, this time using the d20 rules. I wrote up quite a bit of new stuff for it, but it's still recognizable. Jury's still out on d20 vs Alternity, though. Many of the great things about Alternity were incorporated into D&D; the only thing I really wish D&D had was some sort of mechanic for degrees of success.
Anyway, enough rambling. A pleasant trip down memory lane. Hope someone gleaned something interesting from it. ;-)