Really meh. There are some good one-liners mixed in, but most of the characters are really bland and unmemorable. Except for Ms. Quill, she's cool, but the others really leave no impression on me. There's the jock, the outsider, the team "alpha," and the quiet unassuming one.
Granted, I've never been one for teen drama, even when I was a teenager I could never relate to them, and that included teen dramas that are embraced by geek culture like Buffy or Smallville or whatever. That being said, I was quite impressed with SJA and I thought a different take on the Who Universe might be worth a shot.
Of course, it doesn't help the stories of the episodes weren't all that great either. The first one was saddled with the need to set everything up. Introducing the characters, establishing the backstories for the aliens (who come off as the Vashta Nerada with a social order), getting the stuff about the prom, the killings, cameo by the Doctor, and so on. It was all over the place.
The second one had a bit more focus, it just wasn't that interesting. A fairly generic tale of the sports star and the hard-ass coach, when ends up being connected to the alien threat killing people. Endless harping on the death from Ep. 1, which I get it, something like this doesn't just wash away after a few days. But it stands out like a sore thumb when a few other characters are killed off, one of which was someone who had a minor recurring presence during S8 of Doctor Who, and all this is just sort of "oh well, then that happened." The stuff with the robot pretending to be an inspector was kind of interesting, and I assume is setting up something to be explored further on.
I don't know about this show. I'll check out the next one, but so far it's not leaving much of an impression. It's not bad per se, but it's really not that good either.