This series is great and this is why:
1. Animation
Many people complain about the 2D style... Let me tell you something: this is so much better than the cheap CGI alternative they had. There was no way to create more than 1500 minutes of footage for the whole series in the same style as the movie, which is the most expensive animated movie of all times. Great character design, top quality facial expressions,
beautiful backgrounds and colors. The choice was perfect!
2. Voice Actors
We've got the original cast from the movie plus Jeremy Jordan, Eden Espinosa and James Iglehart, among others. They bring TTS characters (old and new) to life, displaying all kind of emotions flawlessly. And their voices... OMG! Wich leads me to the following item.
3. Songs
Alan Menken and Glenn Slater came back to write the songs and it really paid off: Waiting in the Wings (which got an Emmy), Nothing Left to Lose, Crossing The Line, and the list goes on. The songs are beautiful, move the plot forward, bring character depth and the animation on them is just amazing.
4. Writing
The mythology, the expanded universe, the world building and all the characters are amazing. Not to mention these guys had it all planned out right from the start (I can't say more without getting into spoilers)
Watch it!