Quality of episodes and theme music aside, what is or what are some of your favorite opening animations? Eye candy, stuff that's fun to watch, and pretty to look at.
I'll generally like anything well animated or that isn't a collection of episode clips.
.The first intro to the old TMNT series is one of the best I've ever seen. Thundercats is up there too. My sister had kept a Thundercats VHS tape from the 80s, and every once in a year or so I'd watch it. The intro was so cool looking that I'd get all excited about the cartoon...and then the episode would start.
.On the more cartoony side, I also love the Beetlejuice series intro, not the roller coaster one (though still pretty good) but the other one.
.I also liked the MIB series intro. It wasn't all fast action and high energy, but still nicely animated with a unique vibe.
I'll also mention Rugrats (the original version) cuz no one else did. It was visually very different from other cartoons, not toony nor action-y, not much going on but a nice set up. It wasn't flashy or fast paced and it still looked great. I always liked the mirror effect when Angelica opens the door.