The Girl Who Leapt Through Time (this director's previous film) was so much better than Summer Wars, IMO. Summer Wars was just a bit too cheesy, and focused on so many characters that the main two characters had less development than the supporting cast, and made for quite a forgettable affair.
The animation, soundtrack, and production values are all top-notch, and it's got some of the nicest colors and sharpest whites from any Blu-ray I've ever seen before it, but don't expect it to captivate you, at least anywhere near as much as TGWLTT may have.
Speaking of which, TGWLTT is now on Blu-ray, as well, I believe. I'll have to keep an eye out on a deal for that!
I'd also like to add that while Summer Wars can seem and look a bit childish at times, it can be enjoyed by anyone, though the older one is, the more potential cheese factor there will be.
The Girl Who Leapt Through Time, however, is one of my favorite films ever made, and would appeal mainly to adults, whether they like anime or not.