At first, art. SHAFT's trademark, all those unrealistic sceneries and situations that together somehow make sense. I rate the art in this series as outstanding. Just watch one episode and you'll understand.
Secondly, story. This is the only flaw of this series - there was no real plot, basically every episode was a bunch of more or less connected scenes, so we can enjoy the characters.
Since we're at it, characters. Aside from the only significant male character being protagonist himself, this series still deserves 10 in this section. I really liked them all, and when it comes to Erio and Ryushi (hehe) the combination of the way they acted and awesome art usually made me just stare at monitor and smile like a retard. They were insanely cute. At the same time cute like a puppy and feminine. Up to now, I never thought it is really possible.
I'm not saying that Denpa Onna to Seishun Otoko was the best romance anime. In my opinion it hardly qualifies to 9/10 because of the lack of plot. But I'm not saying it was bad at all! I really enjoyed it.
The only thing is that some of you not used to SHAFT style may not enjoy it. All those unrealistic situations, talks, and just the way everybody acts may spoil the fun for you at first. My tip is, don't fight it, just deal with it that this anime looks like this. Treat it like an ongoing joke, and I promise, you will enjoy the series.
Aaaand, that's basically it. I hope I helped you decide to try out this anime, or to look at it a little differently with my kinda messy review. Also, please keep in mind that I'm not native English, and some grammar, vocabular or construction mistakes may occur. If you detect one, write to me, and I'll fix it.
