Now that it's pretty much confirmed that TCats is dead and won't be getting a new season, I guess I can post my thoughts on S2 and the series in general.
As previously stated, I didn't think much of Thundercats S2 back when the first few episodes were airing. I still don't.
Which is kind of sad because Thundercats basically started out with a lot of potential in S1E1. You had the beginning of an epic storyline with the last prince of a fallen empire that seeks the weapons that can repel the evil that has fallen upon his kingdom. Then you have...S2 respectively.
Let's see. What's wrong with S2. Ignoring the fact that a lot of plot points are unresolved or resolved badly (hello flower....), S2 just seemed really badly put together. For example, the Trials of Lion-O; one of the more iconic multi-episode arcs in the original series, wasn't done that well in the new series. The major issue I had with it was Panthro's trial, where the main message was "Cheat". Sure, some could say that the message of that trial was to get Lion-O to use his kingly authority. Not that he had much because all the thundercats constantly doubted him. But the way the trial was put together made it seem more like 'if you can't win one way, then learn to cheat and win another way'. Which isn't a bad message and certainly one more useful than 'keep trying until you suceed' in real life, but I'm not sure it's the type of message you should be putting on a cartoon show aimed towards little children -_-.
And then there are the females of the show... Now I liked Korra because the show had strong female characters. Awesomely strong. Thundercats however, has sad excuses for relationship material. Somehow I doubt the females are written into the show as anything more than an excuse to pair up the 2 male teenage cats. That's how thin their character is. It's kind of sad but Cheetara had more of a personality in S1, but in S2, her status seems to be nothing more than "Tygra's GF" and she never really contributes anything to the plot anymore. As for Pumyra...talk about a dysfunctional female. Seriously, if you ever met a woman like that in real life, do not attempt to woo her or bang her. *yeah, I'm not a fan of modern tsunderes*
There was also a spoiler mid-season about someone who would betray Lion-O and join Mumm-ra. There was some speculation about who it would be over at Thundercats Lair and the three main choices were Tygra, Pumyra and Cheetara. There was the ominous fact that Mumm-ra asked if Lion-O would be the first of his kind to forsake emotion for power. Now, going in, I hoped it would be Tygra mostly because the other 2 choices were really lame. I just couldn't see Cheetara as a traitor and Pumyura was sort of too obvious while Tygra and Lion-O always had that little bit of tension between them that could turn into enmity. Nope, turned out to be Pumyra. And for a really lame reason too.
I'm pretty sure that if Thundercats had a S3, the formula would have been this. "Lion-O meets a pretty nice girlcat, tries to romance her throughout the series only to have the girlcat do a sudden twist at the end of the season and break his heart". Why? Because S1 and S2 ended exactly like that -_- Notice the trend there? Yeah...
As for the boss fight at the end, it was kind of anticlimatic too. I liked how Lion-O and Mummra were fighting it out but everyone lost and then the Wilycats had to come in and save the day...WTF. I'm not sure the writers understand the concept of dramatic fight resolution. The scene could have been done a lot better, but like a lot of the fights in S2, it was half-assed. Imagine if the fight had gone something like the boss fight in Wheel of Time book2, Lion-O and Mumm-ra fighting like bosses while the wilycats summon the allies of the tcats to help fight off the mutants and the two scenes constantly juxtapose so that when Lion-O gets beaten backwards, so do the allied forces and vice-versa. How much cooler would that have been?
In conclusion, there were parts of S2 I liked but a lot of parts that I really didn't like. I liked how Mumm-ra and Lion-O had a sort of banter going on, where Mumm-ra didn't really seem to see Lion-O but saw Leo instead and Mumm-ra actually seemed to like Leo; as far as evil sociopaths can like anyone. It would have been interesting to explore that dynamic. But basically overall, S2? Too bad to watch.