I can take the bad animation and not very appealing character designs but the bad voice acting is the worst. It's great they got the original actors but it feels like they are reading from a script not acting. It's actually pretty distracting for me.
If I recall correctly, some of the original actors criticized that they were just recording lines without context and interaction but the original voices helped immensely to add authenticity to TAS.
I just finished rewatching TAS. What seemed
to be like a mandatory burden on behalf of my TOS Enterprise deck plan project (to cover new locations from TAS) turned out to be a truly rewarding Star Trek experience.
From today's and a spoiled point of view the animation sucks (well, those redundant monsters they often encountered already sucked when I saw TAS in the 1970's...
The overall presentation has a certain naiveté where the target audience are obviously kids of the 1970's and therefore the series also attempts to convey positive morales and ideas to this audience.
if you can ignore these shortcomings and superficialties you may agree that the series' heart and soul is essentially what Star Trek was and should be about (and makes me wonder how Gene Roddenberry could have ever wanted to distance himself from the series).
The protagonists solve problems by using their heads, and not their weapons! If this isn't one of the assets what Star Trek was about, then I don't know.
Frankly, I rather prefer rewatching a couple of TAS episodes over a couple of Star Trek movies. They may not appeal to my intelligence, but at least I don't find these insulting!
And you really have some true gems here. "The Slaver Weapon" written by Larry Niven (!) is a perfect example for logical deduction with a twist at the end of the story that blew me away (...).
"Bem" was a great morality play at the core and featured one of the first visualizations of the concept of dinosaurs that had evolved into sentient bipeds I'm aware of! (because apparently no asteroid hit their planet 65 million years ago).
As in the original series you have some very good stories but you also get your share of bad ones.
Lowering my expectations beforehand definitely helped me to enjoy the TAS experience.
If it's story telling you're interested in, go for it.
If you have to have an appealing box for the content, YMMV.