Been watching Legend of Korra past couple days...and the HSQ just keeps getting higher 
First series was better, IMO. Also, the advancements made in the time between Last Airbender and Korra makes one wonder: What the hell has that society been doing for the past several hundred reincarnation cycles? If it had remained in pseudo-almost medieval stasis for that long, I'd be more lenient, but seriously.
I also dislike three more things about the series. First, suddenly it's not that hard to metalbend or bloodbend. These were two techniques that only came about from intense pressure, where the only feasible way out was through the one or the other. Second, I feel like the whole hierarchy of "Normal earthbender gets beat by metal, metalbender gets beat by purified platinum" is just going to escalate over the series- Suddenly, a metalbender who can even bend THAT is going to show up, until someone stops them, ad infinitum.
Also, suddenly the Order of the White Lotus is just like, a generic open group. The only people in it in the first series are the badass old folks who are masters of their respective skills, and incredibly wise and all that. Now we've got, in that one episode, the White Lotus guys who are basically generic grunts, even though it was implied the Order was secret and all that for a LONG time. Sure, they captured Ba Sing Se openly. But nothing stopped them from just disappearing again.
That was longer than I expected.
Oh, I liked the first one better as well. It's not like the new one is
bad, though.
My impression regarding the technological advancement is that the Fire Nation just kept advancing. They already had the best tech in the first series, and there was no real reason to stop improving. Besides, we in the real-life world were stuck in a similar technological state for hundreds of years - the Avatar world was just stuck there longer.
I'm actually disappointed they treated bloodbending the way they did. Considering how quickly metalbending and lightningbending took off, I was hoping that there'd be groups of bloodbenders who used the power to heal, not torture/kill. I know it's primarily for young audiences, but imagine how helpful bloodbending would be to help keep an amputee or stabbing victim alive until he or she could get more serious care. It's in the middle of an Industrial Revolution, accidents like those are probably more common than they made it seem.
On the other hand, bloodbending was even more terrifying in this series than it was before, so perhaps this was the best way to use it from a storytelling perspective.
Justifying the increase in those difficult forms of bending would require some fan-fictionalizing on my part. From my perspective, it's that just as society and technology continued to evolve, so did forms and styles of bending. Korra made that observation regarding the pro-bending sport, and it seems plausible that after Toph, Zuko, and others laid the groundwork it was simply a matter of teaching the right mindset to willing recruits.
As for the White Lotus, I think their primary purpose was to defend and train the Avatar. After the events of the first series, they probably decided to take a more proactive stance and come out of the shadows a little. They were still fairly skilled for being grunts, but all the old masters are probably long gone.
I think mine was longer