Story: To start this off, I have not seen Kanon so I can't make comparisons or references to it. That being said, I really loved Clannad. It had so many elements that were all done incredibly well. The heartwarming scenes and hilarious scenes achieved just that. I was a little confused with the robot and the girl though. It seemed like it played a huge part in the show but I didn't understand why. I also didn't really accept the whole Fuka-chan part. Those were my only two issues with the series. I loved it otherwise and it has an appeal for a wide range of people. It left you with a great feeling and I would like to watch it again along with the sequel.
Animation: The girls all seemed to have the exact same eyes but with different colors. They had this droopy eye which I wasn't fond of. However, other than that I love the animation. The backgrounds were brillant and so were the character designs. Great colors and very vivid. It was very appealing and Tomoya is quite the looker. The girls are adorable as well. It's a treat for the eyes. The ending also had to be one of the cutest things I've ever seen. It's one of my favorites.
Sound: I love this soundtrack. I find it quite comparable to Air's soundtrack which is one of my favorites. The music fit the scenes and the opening and ending track were lovely. The seiyuus fit perfectly as well. None of the girls voices were annoying either. I have little bad to say about the sound. I would definitely go out and buy the soundtrack.
Characters: What a lovable cast. Usually in harems, I find the main guy to be quite lackluster and boring. I always wonder how he can have this huge group of girls in love with him. However, Tomoya does not fall in that category. He is such a likable person with an amazing personality. Another rare occurrence I found in Clannad is the female cast. I have trouble finding females I like especially in shoujo-like animes. However, I liked just about every girl in Clannad. They were adorable, hilarious, quirky and down to earth. I would love to befriend them and that's really saying something. They also have real reason to like Tomoya not superficial or ridiculous reasons. Even the minor characters are memorable like Nagisa's parents and Sunohara. They all have development as well and far from 2-D characters. I don't really have anything bad to say about them except I still don't understand the robot and girl. I think they're supposed to be important but I don't why. Maybe it's explained more in After Story or I need to watch again. But that was my only issue or this would have been a 10. I really loved this cast.
Overall: If you're looking for romance, comedy or something with quality, look no further. Clannad is a really great anime and something I could watch over and over. It's one of my favorites.