I liked the Nightshade episodes, the Trickster episodes, the Captain Cold episode, and the Mirror Master episode the most. It was tough to buy Captain Cold as a ruthless hitman rather than his traditional Rogue depiction, but it was still fun to watch.
My least favorite was probably the one where Tina goes evil for a while. I just couldn't buy her as a villain even with the circumstances that led to it being out of her control. I also didn't dig the one about Barry's dad's cop past coming back to bite them.
Overall it's still a decent series. Some of the humor and effects haven't aged well, but on the whole it's much more watchable than contemporary live action comic shows like Swamp Thing or Superboy, or later shows like Smallville, Birds of Prey, or Lois and Clark. I'd put it about on par with the first season of Arrow (season 2 was better, season 3 is so far worse).
I love seeing John Wesley Shipp, Amanda Pays, and Mark Hamill coming to the new show. The new show is WAY better than the old one but it's still good to see that they haven't forgotten about it.