Charles commented the cover on Facebook and it looks like you and him have the same opinion.
I like this specific picture chosen for the cover: her pose has a certain confidence and sassy quality which only enhance her sensuality, but none of those factors are too pronounced either, which is good - classy modesty is just as much a defining characteristic of Summer as her raw sex appeal.
The fact that it's not actually revealing (despite being pleasing to the eye) is perfect for a cover because its aim should be to tempt and inspire burning curiosity about what's inside... I think it's also an apt choice because its from a series that highlighted the distinct, otherworldly doll-like aspect of Summer's beauty. I can't think of any other actresses who possess that quality, at least not in the same way.
The colour scheme works well in my opinion; it suits Summer's clothing and binds everything together nicely. Summer is prominent and occupies the space as if she owns it, thanks again to her pose, but there's also enough negative space to balance that and really help her stand out even more. Overall, it's simple and elegant, with just enough sensuality.