The Animated Series is mostly awful, but I love it nonetheless.
If you enjoy "bad" episodes of Trek, buy and enjoy. If not, give it a miss.
I know the studios don't consider it canon, but I've wondered how much was actually contradicted.
No more than how the other Trek series' contradict each other (see the videos in my sig for some examples)
Of the top of my head, "The Magicks of Megas Tu" directly contradicts Star Trek V: The Final Frontier
(in the former, the Enterprise explores the centre of the galaxy, in the latter "no one has ever made it to the centre of the galaxy") and "The Slaver Weapon", being a Trekified rewrite of the Known Space
short story "The Soft Weapon", doesn't fit with the modern Trek chronology. Sulu talks about four Man/Kzin wars, the last of which was 200 years prior to the episode - which would be about the time of Star Trek: First Contact
There have been some huge nods to TOS in live-action Trek:
The young Spock scenes from 2009's Star Trek
were based on those in "Yesteryear" - some parts copied word-for-word.
The Sehlat seen in "Yesteryear" would be mentioned in, and then crop up, in Star Trek: Enterprise.
Kor's old ship which he talks about in Deep Space Nine is the Klothos, from the animated episode "The Time Trap"
I read one of IDW's TOS series and they had Arex in it, and I loved that TAS put two very alien looking characters on the bridge, even if one of those was a cat lady.
Also, Arex and M'Ress, transplanted to the 24th century, have been a part of Peter David's Star Trek: New Frontier
novel series since the late 90's.
Yesteryear was also brilliant.
Indeed. By far the best TAS episode.