The STORY for Denpa Onna to Seishun Otoko was not what I was expecting - and I think it is because of this that I didn't enjoy it much. The premise seems very interesting: a young girl was gone for half a year and then was found in the sea with no recollection of what happened. Now, she thinks she's an alien and walks around with a futon wrapped around her upper body. Uh - sounds awesome! But the execution of this anime was poor and soon this turned into a typical, harem anime.
The ANIMATION was superb - but what do you expect when SHAFT is behind the wheels? I was very impressed with the background effects and the character designs - especially the "alien" girls. They were very cute.
The SOUND was fine... but the OP and the Ending made me want to cut off my ears! I had no problem with any of the seiyuu's, but the music just killed it for me. It didn't feel appropriate and gave it a loli effect that probably wouldn't have been there.
This is a character-based anime, and because of that I was really hoping that the CHARACTERS were going to be excellent like in Bakemonogatari. However, they weren't. Not to me, at least. They all had interesting little eccentricities that would have been endearing had this anime not felt like a fail (to me... TO ME! Not saying this anime was a fail). I did like the aunt, however, and I enjoyed her episode. I felt like they tried too hard to make the characters odd and the character development felt slack and inappropriate.
My PERSONAL ENJOYMENT of this series is more like a 4/10 but the characters and animation brought the overall score up. I watched this in a night and was just very happy when it finally ended. Never good for an anime.
OVERALL, I would recommend this anime with reservations. Be prepared for something lighthearted and fun, and you'll probably enjoy this a lot more than I did. Also, realize you will never figure out with happened to Erio, so just get it out of your head now.