The Superman mythos is pretty incredible when you actually sit down to think about it (strong enough it seems to be fertile ground for endless stories). For one, kryptonite was a great source for "monster of the week" type episodes. But the doomed planet of Krypton, and the clues that Jor-El left on Earth for Kal-El to find was a great source of entertaining story arcs in Smallville. Having those worlds kind of merge with the multiple universes of The Flash and with the Batman-esque rogue's gallery of Arrow is probably going to mean some bigger team ups. And I love team ups and shared universes, because they're lots of fun. Oh and did I mention that with Supergirl comes Martian Manhunter? I really can't wait for the inevitable Arrow, Flash, Supergirl triple crossover week. It's going to be awesome.
Now on my wishlist is a return of Wonder Woman to the small screen and a return of the Green Lantern. At that point, the CW could literally launch a Justice League of America for the small screen, which would satisfy all of my nerd buttons by punching them multiple times. I love the CW. I think it's my favorite network.