First of all, it's not called "Tee Oh Es." It's called Star Trek.
And it's just a matter of opinion. If you're just not a Star Trek fan, you're not a Star Trek fan.
Come on, that's just silly. There are five (six if you count TAS) series and twelve movies and hundreds of books and comics. "Star Trek" is a franchise. This just sounds to me like an attempt to frame TOS as "the one True Trek" or some such by separating it as being "just Star Trek", while of course one has to qualify all the others as "Star Trek: Something Something." People call it TOS to differentiate it from the rest of the franchise, and there's nothing wrong with that.
Interesting to hear how some people like the newer shows but not TOS, since my impression was that TOS is the most popular. I like all the different shows.
I used to think so, too, until I talked to some people more about it recently. My one friend who likes TNG and DS9 very much (in fact, he talked me into watching DS9 for the first time) told me he thinks City on the Edge of Forever is the ONLY tos episode worth watching. =\ Another friend just told me he thinks TOS is unwatchable, too, and that he likes VOY better. This sort of blows my mind.
But I think it could just be kind of like the way some people like new video games are unable to appreciate good older games with poor graphics, too. Like if they've seen TNG and the others, and even the films, and then they think everything in TOS looks too different (or they see those creatures from "operation - annihilate"

) and conclude that it's not worth their time.
I think every series has its own strengths and weaknesses, but I still find it somewhat difficult to understand not liking TOS at all. I also have trouble understanding how anyone can not like the main characters in TOS. [shrug]
I definitely wouldn't go as far as to say that TOS is "unwatchable", nor that there is only one good episode. That said, I do find it far
less watchable than TNG, DS9, or VOY on that shows best days, and find the number of mediocre-to-bad episodes to far outweigh the number of above-mediocre episodes.
To be honest, I don't understand...well, not understanding people liking Star Trek, but not TOS. I do think
respect is important; without TOS, you wouldn't have any other Trek. That's acknowledged. But, it's just a TV show. So is TNG, and so are the others. Each one can - and should - be evaluated on its own merits, as well as vs. the other Trek shows. And if someone just doesn't care for TOS... it just means they watched some episodes of a TV show and came away not liking it that much. That's it. As has been stated in this very thread, opinions vary. Additionally, the shows all have some similarities, but also some
very significant differences. Liking - even loving - any one show does not, by any means, indicate someone will definitely like any of the other shows.
And certainly, the era we grew up in plays a
role. The fact that the special effects are extremely dated doesn't have an impact for me (and I do think that the number of people for whom the effects alone are a big deal is often overstated), but other aspects that tie it firmly to when it was made (the handling of female characters, for example) very much have an impact for me. But I don't even see why that should be treated as a problem. We are all informed by many things when it comes to what entertainment we like.