I was pleasantly surprised by a lot of the show. Of course, I'm not a big Smallville fan, so I had low expectations, despite Geoff Johns' involvement. In a nutshell, things I liked:
The casting. Stargirl could have been better, but still pretty good. Hawkman and Dr Fate were awesome, as were the others who were only shown in photos and flashbacks.
The weapons case
John Jonzz. I don't know if he's ever been shown in alien form, or when he goes intangible, but both looked cool. Also, his newfound fondness for cookies.
"Nice helmet." "Thank you." I don't know why, but that line made me laugh out loud.
Amanda Waller and Checkmate. This has a lot of potential.
The fact that Wesley Dodds' costume/gas gun had a lot of Sandman Mystery Theater influence.
Flashback of Ma Hunkel, wearing her apron with the Red Tornado symbol.
I didn't care for the Icicle. I mean, it's cool that they used the son, making him another legacy character, but he was just kind of irritating.
I couldn't help but wonder if Geoff Johns was purposely making little jabs about Clark not wearing the uniform, like when Lois mentions that Dr Fate's cape actually looked good, or when Dr Fate looks into Clark's future and sees the red cape with the yellow S crest.
I was also disappointed that we only saw certain characters briefly before they were killed. I was hoping to see them in action alongside the others.
One lingering question - There's already an established Black Canary in the Smallville universe. There's one shown in the JSA painting, looking very similar. In the comics, the JSA Black Canary was the mother of the Modern Age one. Are they going to establish the same connection?