I also just finished watching the two-part opening to the new Thundercats series, and IMO it's as awesome as the original series is terrible. The animation is very good, the character and environmental designs are very eye-pleasing, and the writing is very solid. They took a fairly generic, formulaic 80s action cartoon and turned it into a grand fantasy epic with a big emphasis on world-building. They also made much needed changes to the cast and world that make this feel like its own show, and not just a retread of what came before. Characters I despised in the original show (Snarf and, at times, the Wily Kids), I rather enjoyed having on-screen. If the original show was inspired by 80s action cartoons and random inclusions of various mythology, this show feels inspired by shows like Avatar: The Last Airbender and Lord of the Rings. I'll take that pedigree gladly, thank you.
Mumm-Ra actually looks seriously threatening now as well, something he hasn't been since probably the opening arc of the original series. I also appreciate how despite everything that happens in this opening being very bad for the Thundercats, they brought it upon themselves. In fact, the Thundercats as a society come off as pricks overall, so it should be interesting to see how that is followed-up in the coming season. I do have to take a bit of an issue with the music, though. I have to admit I miss the original Thundercats theme song, and this show so far doesn't have a theme song. As for the music, it's good but I heard a couple really familiar refrains in the background music. I swear I heard one of the Star Trek movie theme songs (Wrath of Khan?) when the Clerics were fighting at the gates late in the pilot. There's a lot of potential in this series on display, so I hope the show's writers can maintain this level of quality. After all, the original Thundercats also had a pretty good opening 5 or so episodes (and the occasional excellent story like the Trials arc), and it went downhill pretty quickly afterwards. For now, this is looking to be a very good series that hopefully sets the standard for cartoon revivals.