The first season of Clannad is your average high school anime, maybe with a few magical things happening in it just sprinkled around. When compared to its much higher rated second season, it makes you wonder a bit. However, even still, that doesn't mean that the first season isn't bad. In fact, it's really good at what it does, which is get you invested in characters.
Story: The story isn't the best in this show, I'd say. It starts out with Tomoya Okazaki, a delinquent who's known for skipping class, pulling pranks, etc. He's your average bum. That is, until he meets Nagisa Furukawa, a repeating senior. Besides Tomoya's friend, Sunohara Youhei, Nagisa is the first person to really make an impact on Tomoya's life in a positive way. Slowly but surely, the trio grow as people, meeting new students and creating positive memories just before their senior year ends. The events that occur with this are pretty standard, except for maybe the Fuuko arc. Because of that, and the overall end goal of re-establishing the theater club being the end of the show, I can't see the story being the main focus of the show. It merely served to compliment the character development, letting you become more attached to characters that seem oddly placed if not. If we didn't have something like the Kotomi arc, she wouldn't be as interesting as a character. So while it isn't the focus, the story is necessary.
Art: Being an anime from 2007, I do give the anime some leeway. The art looks nice in certain scenes, like the sakura tree path in the very beginning, and in certain others looks a bit plain. However, when compared to the visual novel, the art is a huge step up. Characters look way better, although the large eyes are still intact, and the overall tones of the characters feel really soft and make the viewing experience feel better. Overall average, but not the main focus.
Sound: Voice acting is always on point as per usual with something that's been given this much time and care. And the music is nice to listen to (it should be if they're going to reuse it in After Story). There's nothing else I can say here.
Enjoyment: Clannad's first season is not perfect, and isn't as engaging as its second, but it still has its merits as an above average school anime dealing with characters who want to build each other up as people, rather than the whole "let's be friends and have fun antics daily".
Overall: Clannad is a nice anime. It introduces characters for a sequel that you are guaranteed to watch, with the added excitement of knowing that your attachment with the characters will only grow as you move into After Story. I wish I had more to say about the first season, but it feels like it's shadowed by the feels trip that is its sequel.