I think it is not a secret that Pokemon is not a high quality anime when it comes to animation and art. It is thought for younger kids and therefore is drawn and animated in a simple style. No match for animes like Death Note.
As Pokemon was drawn by different studios there are differences between the episodes. Some studios were better, some did a really bad job and some have such a unique style that you can tell, which episodes were made by them (like the studio that made "Riddle me this").
Also there are overall differences between the different Pokemon seasons. The colors in season 1 for example were pretty pale in comparison to the later seasons and I did not like the way they drew the characters back then. But they had much more interseting poses and expressions. The movement in the later seasons (especially the Advanced seasons) was not as fluent and varied. It seems that the animation got more simple.
Season 5 is my favourite season when it comes to the art because of the way the characters are drawn. The colors are bright and I like the highlights they added to the characters. "Gotta catch you later" is an awsome drawn episode.
The Advanced seasons are the seasons I like the least. Especially Ash's face and hair look awfull most of the time.
When it comes to Pokemon attacks the DP seasons are best in my oppinion. The attack animations got better and better, especially since season 6, probably because they had to come up with some good looking moves for the contests.
The movies are better drawn and animated than the TV show, of course.
I agree with you, but I want to dissect your points. Hee.
1. The reason why the animation is poor isn't because it's a kids' show (as there are plenty of kids shows that get excellent animation, west and east). It's because the Japanese don't have season breaks/hiatus, so they have to keep cranking out the episodes. In order to that, they have to lower costs, and the product suffers for it.
2. Yep. Different studios cover them, but the less quality ones always seem to do the important episodes (Groudon/Kyorge Part 2 and the BF gathering of Ash's old Pokemon, for instance). Although, they do use the score to compensate, which doesn't help the English version. Heh.
3. Well, the first five seasons were hand colored cel animation, then they switched to computer coloring. So, there is a big difference, there, as many have noted. I don't mind it, myself.
4. Right, the advanced CGI with Attacks from BF onward, which actually works. Rare in most shows that dabble in CGI, but it works well, here.
5. Character design: I do like the first season, even though, it's a tad too angular for my tastes. Compared to some of the oddities we've had, particularly with the Pokemon, I really miss that.
And poor bloated Electrabuzz. Hehehe.