Gene Roddenberry declared the Animated Series non-canon, although a lot of fans and subsequent Trek writers disregard that because it's surprisingly good. Some of the animation is a bit ropy, but the writing stands up pretty well.
TNG had some problems in its early episodes. Firstly, Roddenberry was in charge, and he tended to put his vision ahead of what made for good TV. For instance, he thought that by the 24th century, humans would have evolved beyond interpersonal conflict, which doesn't exactly make for compelling storytelling. Secondly, a lot of the scripts were recycled from the aborted Phase II. Thirdly, they ran into a writers' strike in the second season. And in general, they were trying to create a show with its own identity in the Star Trek universe at a time when most fans viewed the concept of a non-Kirk Enterprise as blasphemy.
There's still some great stuff in there, 'The Measure of a Man' being a case in point. But I'd say the series as a whole only really got good around season 3, when Roddenberry stopped running things and the other producers figured out what they were doing. My personal favourite episodes are 'Best of Both Worlds,' in which we see for the first time how truly alien the Borg are, and 'Darmok,' in which the crew encounter a species whose culture is so idiosyncratic that communication is impossible, and Picard has to form an alliance with their captain to save them both.
