I did like it a lot overall but...
And it isn't because Thoma didn't end up with Helga. In fact I think Thoma telling Helga that she will find Soran some day was a nice unexpected touch although in my heart I would rather Thoma have been with Helga. But if I got to see Helga be happy 10 years later. Then why the hell did they not show me what happened to Thoma. I wanted to know that he ended up happy as well.
Besides Thoma I would also really have really liked to find out what happened with some of the other characters. What about Agi, Hasmodai, and Soleto (I forget all their names.) Did Mel and Palza ever find each other? (I mean if Tina can find Soran again.) What about Chitto, Dumas and the detectives. Personally only focusing on Helga's future was a real disappointment to me. If they were going to do that then I would rather them not show any future at all.
I am trying to wrap my head around if I liked the series enough to buy it. I thought the plot twists and the overall story were excellent. My favorite parts were definitely the flashback sequences on Greecia, episode 23-26 and when Helga, Chitto and Thoma were on the Island and at Thoma's home. I did feel some of the characters were a little flat at the start but they all did grow on me. And Thoma I loved pretty much from the beginning. He was my favorite throughout.
I do think the anime was lacking in character development. There were certainly some great character ephinanys but a lot of the characters' development was sparked by some huge event. Personally I like it more when characters develop a little more slowly. However I can forgive Fantastic Children for this a little since the anime was only 26 episodes and the show did such a good job with plot. It is certainly was a very well told story although I would lie if I said I wasn't a little disappointed in the end.
But I am still really glad I watched it. I also think this anime is heavily underrated. The people who watch it rate it highly but barely anyone actually watched it. I mean I can barely find anything about it online. :/
Edit: OMG Souten No Koumori is out and it's so awesome. XD