This pair of short series are filled with a fair amount of action, with a splash of mystery and copious amounts of fan service.
Just your basic T&A anime.
Over at ANN the fans give these a 6 for the first series and a 6.7 for Gravion Zwei. Personally it's hard not to agree. The shows have rewatchability but there are far too many cliches for them to be anything but mundane. I have both series and I don't feel ripped off but I don't feel like I got any bargain.
Some people are going to enjoy Gravion for either the Mecha or the fans service and a few will love it for both.
I liked the character designs but I like any yummy looking girls.

Linkage to the Anime News Network Gravion pages

Linkage to the Wikipedia Gravion pages