If you're a fan of age of empires 2, you should definitely try 0ad http://play0ad.com it's open source and multiplatform
0ad is excellent for quite a number of reasons, first is the history it teaches you, the other is you can grab it @ https://github.com/0ad/0ad and https://github.com/0admods and really tinker w/ the AI and build meshes,models w/ Blender, +1 for 0ad