Well, Avatar: Secret of the Fire Nation just aired over here (actually it's been like 5 hours already) and I felt like giving my thoughts on it here.
Let me start by saying the title is really misleading. All they had was a gigantic drill to penetrate the walls of Ba Sing Se. Not much of a secret there. I was expecting more of Iroh's past or something related to the attack from the past.
The Serpeants Pass
+ Suki and Jet returned, even if for a short while.
+ Toph had her moments, especially a kiss she accidently gave to Suki after she rescued her.
+ I REALLY wasn't expecting a birth scene near the end of the episode. They didn't show anything explicit but still...
+ Aang unable to convince the passport lady to get on the ferry + the fake avatars + Toph basically given the tickets = Best scene ever.
+ Aang's Gang attacked by... Rayquaza!
- Emo Aang. It only lasted for this episode but still, he was really annoying.
- Toph/Sokka hints. I don't dig this shipping, and I doubt I ever will. Toph is too cool of a character to just suddenly start falling in love.
- Not enough Zuko.
- No appearance by Ozai's Angels, but they make up for it in the second part.
The Drill
+ Ozai's angels, but most importantly...
+ Ty Lee!!!
+ The fight scenes were really well done in this episode, especially Aang and Azula.
+ Aang giving homage to Fantastic Four by turning his hand into rock, resembling the fist of Ben Grimm.
+ Sokka is a huge pimp apparantly. Suki, Princess Sue, Toph and Ty Lee. What a terrible choice this guy will ultimatly have to make in the end.
+ Jet finds out Zuko and Iroh are Firebenders. Oooh, friction...
+ Surprisingly, the cliche/ignorant dumb general was highly amusing in this episode, despite being annoying on all other episodes. Maybe it's just because this episode was made of ten kinds of awesomeness.
+ Toph proved her valuableness again by sneaking them into the drill, while the L33T Earthbenders got pwned by a dancing circus girl (;D) and a bored man-chick (:-\).
- Mai did absolutely nothing in the episode besides beat up a few soldiers.
- Again, the drill was not much of a secret and thus, a letdown.
- Not enough Ty Lee
Overall, it was great with only a few flaws. Also, I'm glad to hear it'll start airing weekdays starting Monday though it won't really matter to me since I'll be getting the Book 1 set by then.