I loved this game! Yeah, it's different, but it's a good different! There's no reason not to get it!
Think about it, there is a faction of just Steampunk! The Vinci Clockwork Men are the coolest units in the game! Then you have the Alin who captivate you with the "Arabian Nights" feel. And lastly, the Cuotl have some of the most interesting tactics available to them, being Mayan/Alien hybrids.
The Campaign was fun and the story left me on the edge of my seat. Now, I will admit, it wasn't a movie worthy story, but it was entertaining nonetheless.
The graphics are really good for a bargain bin game, and it seems that many hours were dedicated to its creation.
Now, I've never played the Rise of Nations games, so I can't compare this game with those. But as an avid RTS player, I can say that this is a breath of fresh air. I like how the factions are not just carbon copies of one another, all three have very different ways of accomplishing the same thing.
So, in short, this is a game that you should buy for $20 at Wal-Mart. It's fun, it's fresh, and it's worth your money.
(I can't wait for a sequel!)