Gravion is one of those animus that when you hear the story you think "Well this could be good" and then you watch the series and notice the millions of places it just went completely wrong.
Story - 3/10
The basic story tends to be something that could have been turned into something good, brother searches for his lost sister and finds out she was chosen to be part of a secret mecha team thats protecting the earth, but then went missing. As time goes on we learn the robots are created by Mr. Sandman and used to fight his brother who are sending the Zerevire to destroy the earth.
What happens is the creators forgot all of this and focused solely on finding as many ways to throw a jiggling boob at you or put a girl in a erotic position (the one girls robot is designed where she has to sit in a way only fit for a porno) Now repeat the same actions of 2 minutes of minor story progression, attack on the earth, same animation and terrible song to show robots combining, defeat bad guy (which every episode they needed to add a little something new, Why not just be the best you can and destroy the problem on day 1?) and celebrate.
The best parts of the series are when they get away from anything having to do with the main story, such as the beach episode or Eiji leaving and hanging out with his friends.
The series ends with nothing being answered in the slightest, I really believe the forgot what was in episode one and after completing the series realized everyone would hate it and made Gravion Zwei to answer the questions never answered, which did and didn't happen.
Animation - 6/10
Everything was pretty well drawn, i think they liked it so much from episode one they then decided to use at least 3 minutes of animation from that episode in every one afterwards.
The Zerevire were also all pretty different and well made, though you can see a lot of influence on them and the Gravion Mecha from other shows.
Sound - 5/10
The Voice acting was dubbed pretty well and none of the characters ever got to the point of just getting annoying.
The downside of the sound is the song played during Gravion's combining. I get how many Anime rock songs can sound cheesy, with their use of english phrasing in random sections, but in Gravion it just seemed deliberately bad and possibly an inside joke that helped dig the show deeper into a hole.
Characters - 2/10
I don't remember any character being built up in this first season. We really know nothing about the whole cast. We get a bit of background when Eiji goes to meet his friends, but again this seems like something they forgot and used as an excuse to make season 2.
Again this seemed like a promising show with a decent story, it could possibly be cut into an hour long stand alone combining both seasons with a fight or two, and it would be much more watchable, but as it stands it doesn't seem to be there to please anyone who wants more then repetitive fights and boobs.