Star Wars Empire at War combines a great combination of ground and space combat which not only looks great but also plays well.
The game works around the idea of a galactic map with planets that you control. these create a general map that you have to conquer, each planet can change control to whoever conquers it and has two levels of defence that you can have.
Ground defence allows you to have fight in traditional RTS ways where you have to eliminate the hostile forces to capture the planet or stop an invasion force.
Space combat allows you to bring large or small ships into combat using RTS gameplay, this creates great combat and gives you the oportunity to play as you want. there can also be a space station and defences that you can build / destroy making space combat vary in each fight.
the game in general is good fun for anyone who likes RTS games with a unique take on the genre. i find that it is enjoyable and the game has its own fan made expansion which completely overhauls the game and changes the empire and rebels to republic and federation. This allows for an entirely new type of gameplay as the new units have far more weapon spots and units which makes your screen light up with turbo lasers.
the expansion however can run a bit slugish if you go insane and spam battledroids as the game tanks and doesnt run too well.
in general i would say if you like RTS conquest games then give this a shot, its pretty cheap now and the free expansion Republic at War allows for a near whole new game.