The racism and sexism in TOS has been an issue for us watching it. It is much more mild than other shows of its time, but it is still there. I also watched TOS as a small child and most of that stuff went over my head, but now watching it again in my 40s it really is cringeworthy. That said, I know there are a number of key episodes that should be watched, and I know some of these elements go away (or lessen) as the show progresses.