this is an awesome game. too bad the G Generations series doesn't get out of jpn more often. here in asia, people have been like flooding the bbses for this for days. i've read over a dozen topics wondering when it'll be dumped.
anyway, this is a s-rpg, much like the super robot series, except it's better.
the graphics are much better than D (though d's pictures are bigger) and the system is very very complex. however, to really get enjoyment out of this game, you have to know gundam, and i would recommend knowing at least a bit about every gundam series.
system-wise, you can tackle this game like a normal super robot series, but you can also form teams of three.
example: a really tough enemy. you merge with two other robots in a squad of three, get much damage and accuracy. you severely damage him. to counter you, he gets into a team of three. you have your battleship open fire on him. to escape the huge damage that your battleship may do on him, he splits up his team again. you encircle him with three of your robots, and take over his robot.
you can use that captured robot, or split it up and sell the parts, or use those parts to further upgrade your current robot (or mobile suit (MS), as gundam lingo goes). you can also merge two or more MSes together to develop a new series of MS. et cetera.
in short, awesome graphics, decent story (twists the gundam plot to fit all of the gundam storylines though), and a really really cool system.
Edit: BTW, this game is very Gundam Seed heavy. lovers of other Gundam series, you were warned.