Personally, I find that the whole show can be decent if you separate it enough from the books, and if you go in KNOWING that they changed major elements.
I would have disagreed, but the fact that it did gain fans (including people I was at school with) who didn't read the books proves you're right.
Hmm, I don't think so. I could cope with them changing some, or even a lot, of plot elements, but IMO it was really poorly done in acting (for the most part), technical work (as someone else has said, the hawk still had the handling straps on), and just kind of lost the spirit of the books. They needed a bigger budget, mainly. I mean, the special effects were so poor, especially the Andalites. Does anyone remember when v3 and Ax arm-wrestle instead of tail fight?
Although I thought the actor playing Ax as human did very well 
Oh yes, just watched that one today, one of the worst on screen battles ever. Not helped by the actor playing Visser 3 hamming it up like theres no tomorrow. You'd think the director would have asked him to bring his performance down a little.
Overall I think that good writing and good performances can triumph over bad effects over bad effects, however Animorphs fell short in every department.
One thing that annoyed me was the amount of stuff that they did that was in direct contradiction of the books. Rachael's claim that they always used to hang out before or Marco identifying Tom as a controller because he as playing with his ear (I'm pretty sure there was a line in the book that said “It's not as if controller go round playing with their ears). There must have been more, but that's all I can think of so far.
Another problem was the way in which the chose to accelerate the stories. I get that one book per episode can be difficult, but it was done in a way which made the Animorphs look incompetent, not inexperienced, flat out useless. The one that sticks in my mind was when they did The Visitor (episode 4?), they successfully catch and morph Chapman's cat, but fail to lock it up so that it can just wonder back in and blow their cover. It's a basic mistake and one they didn't make in the books.
Then there's the disk. What were they thinking? When it was first introduced I assumed it was going to be a plot device which would give them useful information when they needed it, but no. They had it for about an episode, then they lost it (the incompetence rant again). I mean Jake just dropped it in the Yeerk pool or something, they never even said when, it was just 'oops I lost it'. Interesting side fact though, something that passed my by when I first watched it (ten years ago now!), Ax says that they lost Elfangor's Hirac Delest.
The casting was also an issue. There have been occasions where good casting can carry a series above the poor effects and low production values (although not flawed writing). However the casting didn't totally work either. Briefly:
Jake: Best piece of casting of the series, Shawn Ashmore really captured the character and it seems appropriate that he's had the most successful post Animorphs career.
Ax: Paulo Costanzo did very well in the role, he was suitably awkward and was able bring out the alien nature of the charter.
Rachael: She might have been good, but the scripts and the direction didn't do the character justice, never really brought out here warrior nature.
Cassie: Same problem, she did a good job with what she had, but never really got the the heart of the character.
Marco: There was just something missing from the performance, he delivered the lines, but he just didn't have the wit to go with them.
Tobias: Wrong wrong wrong. He looked and acted nothing like the Tobias of the book.
The adult cast was generally not particularly well developed or used, but I would like to give a quick salute to the best adult performance, Richard Sali as Chapman. I thought he played the character really well, showing the classic villain, the mock humanity in the scenes with Mellisa and then actually getting some sympathy for what he had to do.
Sorry I've rambled a bit there, but hopefully I've made some valid points.
