At first I was skeptical as to just how good this series would be and the 50 episode runtime was a bit daunting however I began watching anyway as it seemed the most interesting out of the series I have waiting. I can say that I definitely wasn't disappointed.
I'm sure you've read the synopsis so I won't be mentioning that here. The story moves quicker than what you would expect from such a long series and this is a good thing as it minimizes any time where it would seem to be boring. This is even more impressive when you realize that there
is next to no filler and what filler there is was entertaining and worth watching. The context of the story and the way it evolves isn't over the top or unbelievable, it unfolds at a steady pace the entire time and doesn't ever feel rushed or drawn out either. I see that a couple others have said that at times it is hard to follow but that isn't the case at all if you're paying attention and overall its an enjoyable journey with a satisfactory ending even if it left you wanting just a couple more answers.
The art is definitely above average, the animation is smooth and the colour scheme works well. It is a great support for everything else and the variation in quality across the span of the series is minimal. There were times when a certain lack of shading was noticeable but they quickly passed. Its not the best around but it is very good and considering the length makes it all the more impressive.
The sound is the only section i'll score a perfect 10, it really is outstanding. The music from the openings to the endings and everything in-between is enjoyable and not something you'll get sick of. Every track seems as if it could have been made to be used here and truly makes part of the show what it is. Sound effects and the like are perfectly acceptable, definitely above average. I haven't heard the dub so I can't comment on it but the Japanese voice acting fit well and no characters voice felt out of place. Overall a very pleasing experience.
The characters are great, you won't see any cardboard cutouts here, each character is multi-dimensional and all add to the story. Eureka at first seems distant and not quite developed but thats exactly how she's meant to be, you find yourself waiting for scenes where she and Renton interact with eachother for this is where alot of entertainment comes from. Seeing her grow as a person from that is quite something. That leads me to Renton, an average kid by all means, at times its downright annoying how naive and childish he really is but he learns from it and by the end you can truly see how he has grown. With all of this you may be asking why I rated it only an 8, thats because of the three kids, maybe I just dislike kids altogether but they cry at the drop of a hat, mess things up due to their own selfishness and are just a plain annoyance, I found myself becoming slightly irate everytime they were on screen. However i'm sure thats how people sometimes feel around real kids as well so if they were given just a little less screen time I guess I could have brushed it off. Overall the character development is really great especially concerning Eureka and Renton, further more apart from the kids I didn't find myself disliking any character which is a testament to how well made they all really are.
I watched the series in three days and it never felt like it dragged on, I was always eager to see what came in the next episode and overall I really did enjoy this series. It just has the feeling of being enjoyable, taking you on a ride and you find it hard to leave. Once again I felt the kids detracted from this but whatever shortcomings they bring are immediately made up for by the rest. Enjoyment level for this series is high.
In the end its an interesting, enjoyable and great series. Don't let the length put you off, if you watch anime then this is something you should see.