I'm not a big fan of mech shows. I watched Gatchaman (as Battle of the Planets) because it was the best cartoon on TV at the time. I never saw so much as a single episode of Robotech and the first mech series I actively liked was Patlabor; and then, after that, Gundam W.
(At least, before all the homoeroticism became bleedingly obvious to me. But that's mostly in the dub version, anyway. And for the record, I think it was Qatre and Trowa, not Duo and Heero.)
Mechs don't really appeal to me much. Machines that size are impractical for a host of reasons, and I generally just can't set aside my prejudices enough to allow unalloyed entertainment; there's always this little engineer voice in the back of my head wondering what the legs are made of, to be so slender yet able to support so much weight; and why the pavement doesn't cave in under the load of the machine, and so on. The Gundams in Gundam W clock in somewhere around forty tons, each, for example. In reality, giant mechs are pure fantasy; there's no way to build one which looks like the ones in the shows without all kinds of exotic technology.
There are some mech series which do it right. Some mechs have huge feet, to spread the load; but those mechs look horrible.
I approached Gravion from a different perspective, though. I figured that the show was going to be, basically, pure fantasy; approached from that angle--instead of treating it like it was science fiction--it was a lot easier to suspend my disbelief. I simply put my brain into Star Trek mode, and that made the difference.
There is no resolution to the larger stories of Gravion; it's purposely left open-ended for the sequel series, Gravion Zwei. But the smaller story arcs which drive the episodes in this series were concluded in a suitably satisfying fashion. (Gainax could learn a thing or two from watching Gravion. It may not be animated art for the ages but at least it ends decently!)
I started viewing it with low expectations and was pleasantly surprised. It's pretty good.