I adore the original show, and like pancake3 find that many of my favorite episodes are those often dismissed as “filler” - character-centric episodes like “Sokka’s Master,” “The Headband,” “The Cave of Two Lovers,” or “Tales of Ba Sing Se.”
That being said, I also really loved the first season of Korra.
I agree that it suffers somewhat from the lack of time to breathe. Korra S1 could really have done with an additional few episodes, if only so that some of the plot could have doled out over a longer time, allowing for more small character moments of the sort that made the cast from Avatar so complex and enjoyable. However, despite that, I also think that Korra’s almost relentlessly brisk plotting gave it a great sense of urgency. Now that the full season is available on DVD, it’s a ton of fun to blast through from start to finish. The story is propulsive and exciting, with shocking twists that still nonetheless feel utterly correct in retrospect, and the animation and music are both a giant leap forward from Avatar (which was no slouch in both departments, itself).
And I don’t think the characters were paper thin. Korra herself is a wonderfully nuanced protagonist, equal parts brash and vulnerable, and wonderfully acted. I also think that Tenzin, Asami, and especially Lin Beifong are some of the best characters the Avatarverse has produced - they all feel like fully realized people, full of strengths and flaws and contradictions and history.
Amon and Tarrlok made for great villains. I really dug the expansion of bloodbending, a horrifying concept only briefly touched upon in the first show. And the scene pope_hentai cited from the last episode left a terribly, wonderfully unexpected lump in my throat. It was the same feeling I got watching Azula’s downfall in the series finale of “Avatar,” when she is chained against the grate, broken, and screaming her despair into the sky. I love when characters that we’ve been rooting against all this time get their comeuppance in a way that we, the viewers, actually empathize with them, rather than celebrating their defeat.
It is unfortunate that Mako and Bolin don’t get the same level of development. The former is rendered pretty unlikeable by the focus on his love life (something that only works if the audience is first given reason to actually care about the character in question). And the latter, IMO, never really transcended the sense of being “Sokka 2.0.” That being said, I think there’s plenty of room for these two characters to grow in coming seasons, and look forward to seeing where the writers take them. And after four seasons of pretty awesome television, I do trust these writers.