Well of course...
Actually, I heard that at least part of the second season overlapped the 1988 writer's strike, which gives them an excuse for not improving the storylines much from the first season. Overall, the third season was an amazing improvement over the second, and I agree that the fourth was their best. It was steadily downhill from there, though.
Growing up I always thought the funniest moment in the original series was when the cascade of tribbles fell on Kirk. But then, that was supposed to be funny. If we're talking about unintentional moments, there are too many to choose.