A few things to rave about first: I'm loving the probending announcer/opening recap narrator. His voice is just enjoyable and really sets that certain tone for the show. The new friendship of Naga and Pabu is adorable and the series still has those amazing goofy faces it's great for.
On to the more serious topics of the episode: The introduction of chi-blockers is a very serious threat to the series. It really adds to that industrial era feel in that machinery is taking over nature and the natural ways to do things. The blockers are also a powerful enemy - I'm not sure the "good" gang is equipped to deal with them at present, even if Korra is unusually strong (anyone else notice last episode when she picked up Tenzen and all his kids like it was nothing?)
I get this distinct feeling that Amon is someone we met in the original series, or whose parents we met. I'm very interested in him and his backstory. Props to the writers for making an intriguing villain. Now if they'd just make him more multifaceted to actually hold my attention. No one likes a one-dimensional character.