The bars span the full width of my screen, which makes them hard to read. There's very little text, and I have to interact with each option to see details about a flight, which I find annoying if I just want to scroll through.
Also, the screenshot I gave above is a pretty tame example. Compare it to another search where there are more airlines in similar price ranges - http://i.imgur.com/e7VJq.png
Again, I'm not sure what details you're looking for; the stuff I care about (cost, departure and arrival time, rough length of flight, where it connects) is all right there.
As someone who lives in a city that's always one connecting flight away, I can't tell you how many times I've almost booked a flight only to realize the one that's $5 more on the same airline connects in a city more on the way and with less layover time, and Hipmunk does a far better job of communicating that to me then a traditional list.
That being said, I'm not using it exclusively yet (I usually check both Kayak and Hipmunk just to make sure I'm not missing something), but I really like that somebody is trying to do something different and (hopefully) enjoyable in flight search.