Aldnoah Zero is one of those shows that is stuck halfway up the ladder. It hasn't reached "great", but is out of reach of "bad".
While there are better alternatives to this show (Code Geass, and Neon Genesis Evangelion, for example), that doesn't mean you shouldn't watch it. It has enjoyable fighting scenes, a pretty neat soundtrack, and interesting characters, and quite simply, is entertaining.
The disappointment lies in the direction of the show. It started off with a riveting premise (I actually thought it would be another Code Geass), but it fell short of expectations, which is why I think this show receives substantial amounts of hate. Just to clarify, the ending wasn't bad, it just wasn't satisfying.
So if you're bored, and can't find anything to watch, you might as well settle for this average show, just don't expect much. Enjoy it for what it is.
Review of Aldnoah.Zero
