When I've read the synopsis of this movie, I was thinking it was essentially about internet issues. But after watching the whole thing, I realize it's basically a family movie about how family is important and how together we can pass through difficulties.
So I didn't dislike it, the animation and all was good and I kind of enjoyed it. But I was clearly expecting the plot to concentrate on internet issues, and from this point of view I can't help but to be disappointed. Since this seems not to be the topic of the movie, the internet aspect (through the OZ system, the virtual/real life) is hardly treated, or is represented with a dualist vision (good people fighting an evil virus).
So I can't really be tough with Summer Wars since I've misunderstood the target it was aiming at. I just can say it's a good movie I appreciated even though I was expecting something else from it.