Upon light perusal, the story is pretty cute. A little boring, but nothing terrible. It's when you start thinking about what's happening (even just a teensy-tiny bit), that everything falls apart at the seams. What the dickens is happening and why?
How were Nagisa and Tomoya able to meet Fuuko in the first place? Scratch that, absolutely nothing in Fuuko's arch makes any sense at all. Nothing. When I wasn't rolling my eyes or staring dumbfounded at the screen, I was pretty impressed by this accomplishment.
How is Kotomi able to survive? Her financial situation is nonexistant. Why don't anyone's motivations make any sense? What does playing a basketball game have to do with establishing a club that has nothing to do with basketball or anyone on the basketball team? The entire show is full of nonsense and poorly-disguised plot-holes. It's pretty obvious that Clannad's creators think their audience is full of idiots who won't bother questioning anything that's happening. I'm not sure why nobody seems to be bothered by this.
One of the only interesting plot threads (Tomoya and his father) was completely ignored. In a very hentai-esque manner, it was used only to get Tomoya into Nagisa's house, then tossed aside.
Clannad had some funny moments (most of which were in Fuuko's arch), but I don't really like KyoAni's sense of humor, so that's another strike against the series, for me.
OH GOD MY EYES!
OH GOD THEIR EYES!
Seriously though, I will never understand the character designers' reasoning behind- "We've got to make her super cute... Let's make her eyes take up half her face!". They look absolutely terrible and alien-esque. Does anyone actually find that attractive?
Aside from the horrendous character designs, the animation was pretty ok. Animation was fluid, and the backgrounds were nice. But the thing is, Clannad is a pretty character-driven anime. There are hardly any times when no characters are shown, so regardless of how nicely everything else was drawn, their disturbing faces ruin everything.
Against my better judgement, I found the ED (the one about the Dango Family) absolutely adorable, and never skipped it once. The OP on the other hand, I couldn't manage to listen through the entire thing a single time. It was cringe-inducingly bland. I can't remember any of the insert songs, so I assume they weren't very interesting, either.
As for the voice actors: Well. The males were alright, but virtually every single female had an obnoxous too-shrill squeak. And they talked a lot. So some episodes were constant squeaking as they just tittered amoung themselves uselessly for long stretches of time. It was unpleasant.
Tomoya was alright. I can understand why people like him, especially in comparison with every other male harem lead in existance. He is significantly less useless than them. But he wasn't so great as to have a gaggle of mindless girls (one of each major character trope, how convenient!) following him around blindly and doing whatever he tells them. Hard labor? No problem! Join some club I don't care about? It's not like I have any motivations of my own!
And now we get to Nagisa, the other main character. Ugh. The girl never said anything of substance throughout the entire show. All of her dialogue could have been replaced by loud buzzing sounds or various birdcalls, and the series wouldn't have been significantly altered at all. She was offensively dull. Nagisa was also the worst ill-girl ever, as her health was only ever an issue when it would add dramatic tension to the plot. They made a huge deal of it at the beginning, and then the next episode she's acting like a normal girl and nothing in the world is wrong with her.
The creators tried to spice up the giant cast of moe archetypes by giving them all "kooky" and "unique" quirks. So-and-so is a terrible violinist! What's-her-face is obsessed with starfish! How novel! But the thing is, all of these "interesting" traits were shallow and hardly related to the character who had them. You could take all those traits and randomly re-distribute them amongst the cast, and it wouldn't make a lick of difference. They didn't turn the girls into deep characters or have any discernable impact on their personality or anything.
Did I miss something? I honestly cannot understand why this is one of the most beloved anime series. It was ugly, derivative, and predictable (in the few flashes of clarity when the plot was sensical).