I liked it. Like, really liked it.
It's got the same tone as The Flash and the special effects are pretty decent. I like the backstory as well, as I was quite confused how she could be younger than Superman (who's never referred to by that name, he's just referred to as "him" or the "cousin"), but obviously they'd go down the road of having her trapped in the Phantom Zone.
The pilot was obviously focused towards bringing Supergirl to life and while it'll unfold over the season, I liked the focus between Kara and her sister. There were a few humorous moments, too. I'm not entirely sure if I like Winn (delivering the worst one-liner ever) crushing on her just yet. The guy who plays Jimmy Olsen seems decent enough. Cat Grant's actress is all right, although I'd rather see more of her to make a full judgement. I also like her sister and her involvement in the underground organisation was a nice twist, even if it was slightly predictable.
It's also nice to see they haven't revealed all her powers just yet, but the important ones. There's only super strength, flight, super hearing and heat vision. I'd very much like to see more flashbacks to her time with the parents her cousin put her with, although I know I've only just got past the pilot and will most likely get my wish over the season.
The last scene of the episode had me the most intrigued, though. So Kara's aunt is going to kill her and said she "escaped with her cousin". At first, I thought it might have been Superman's mother, but immediately took it back when she said that.
Her character was pretty infectious and whether you liked the trailer or not, I'd check out the pilot if you can.
Everything about the episode is
nailed right here in this spoiler-free review.