I both liked and disliked this series. I thought it so impressive that they got most of the original cast back together, had DC Fontana running it, and had some really top-notch writing talent. Also, with animation, there was the promise of doing all kinds of interesting special effects that weren't possible with TOS.
The problem is that the animation budget was so limited! I didn't mind that sections of scenes were recycled, something which also happened here and there in the original series, but that the Filmation art & technique was just so mediocre. As in, not nearly as interesting as some other studios were putting out, such as Depatie-Freling. Even some H-B series had far more interesting art & backgrounds, like Scooby Doo.
Another problem is that the weak budget meant that poor Jimmy Doohan had to voice virtually every male character outside of the core cast. Similar with Nichols & Barrett having to do all the extra female characters. It got pretty identifiably ridiculous even just a few episodes in, and was a shame, because Hollywood's always had an amazing stock of versatile voice actors that worked surprisingly economically. (Mark Evanier's blog is a good place to read about that sort of thing)
OTOH, I sort of enjoyed the animation bloopers, and there were many. One of my favorites was the way background characters would sometimes be larger than foreground characters. So, interesting to read that many of such 'bloopers' were in fact by design:
"There were also only so many layers you could use before the colors started changing. Sometimes, you'll see a missing leg or something like that. It's not always a blooper, it's just that they only had so many cells that they could use."
"If they wanted to have an animation on top of whatever was happening, sometimes they'd have to sacrifice something that maybe nobody will see this," states Harvey. "At one point, Scotty's doing something and he has no legs. He's just a floating torso. For me, that's part of the charm. It's just the idea that this wasn't just like, 'Oh, we're being caught careless.' It was, 'We have to make a decision on how we're going to do this.' That was the process. That's a very abbreviated version of that process.