"If you still have TA: Kingdoms get this"
It works. That was the main thing about this game. On the computer that I originally had TA: Kingdoms on alone when I installed this add-on the game actually started to work at a good speed and without troubles. Computers now are even faster so it runs flawlessly.
The actual mechanics of the game are stunning. The 5 races though completely different are completely and perfectly balanced. You will not be guaranteed victory by simply choosing one race over another. As with the original TA you need strategy to win. And a lot of it.
Also on one occasion I actually had a "divine intervention." That was one of the most exciting moment in a game I've seen. Suddenly lots of flashing and exploding and once the dust settled all that was left was half of one base and an almost dead God. (These were huge bases too.) The game was at more or less of a stalemate and that ended it in less than 5 minutes.
Complete lack of a community or support for the game. It came out a little too late and all the people who would have enjoyed this game had already moved on to other games.
The other tiny problem was with a couple of the super units. Namely the Giant Orm (it looked like a giant football with little feet and huge jaws). It was amazingly powerful. It could completely destroy an entire base if left on it's own, unless there was a single ranged unit attacking it. So frustrating to lose something so big and powerful with such ease.
The Bottom Line
If you have TA: Kingdoms still kicking around somewhere pick The Iron Plague up. You can get it for $5 and it'll show you what the game was meant to be.