Earth 2160 is the last in the line of Earth games. In Earth 2160 they really changed the way the game worked and played. This is especially true of building construction. In the other Earth games construction was like other RTS game many separate buildings laid out on the ground. In Earth 2160 it is more of building a tower with each component built on the last.
building units was fun and adding the items you wanted to your designs was always fun and needful in the game.
I found Earth 2150 the best of the lot but it still had it flaws. Not easy to follow the Campaign, building many units to see who's was more powerful, and the one thing about the Earth series is the uselessness of Boats in the course of the game.
You might enjoy going back a bit to the 2150 stage of games. I am considering getting the 2150 series, but I think I will likely stop there.
Also, if 2150 can be played online still it can be a blast.
Enjoy!