You have up to nine planets, and you're only allowed to build some facilities, and must make fleet to survive
Some features I bring from
www.ogame.com are income scale from buildings, fleet-only ship management, wrackage gathering ...
features from Space Empire are: the races, the form of the tech tree, ship customizing, trade in alliance ...
I played ogame for a year with some friends, but it turns crazy: the best stay the best, and the other ones, stayed as farm for them