Eh, I think most of the problems with it were simply factors of not having a big enough special effects budget, not being able to get/train the right animals for morphs, and being constrained by the half-hour time slot. And I can't bring myself to criticize it based on any of those factors; I mean, come on, they did their best. And almost all of the show's problems can be traced back to those three things.
I guess there were only two things that pissed me off about the show:
1. The changing of irrelevant details for no other reason than to be different
-Jeremy Jason McCole ---> Jason John McCole
-Maple and Ginger instant oatmeal ---> Maple instant oatmeal
-"I'd like a happy meal, with extra happy." ---> "I'd like a cheese burger, hold the cheese."
Don't know why those things ticked me off, since they're pretty irrelevant, but for some reason they did. I guess I didn't see any reason for them not to stick to canon.
2. Misportrayal of the characters
-Rachel's actor was terrible. She talked brave, and everyone around her said she was brave, but she did not act brave
-Tobias's family life got downplayed, which in my opinion means that the show missed the entire point of him being a hawk; it wasn't an accident, or something that happened because he liked to fly, it was to escape his sucky life as a human
-Ax's humor got played up, and his warrior/honorable characteristics got played way down
Jake, Marco, and Cassie were all pretty good portrayals, but even they all acted out of character sometimes.
I just watched the show pretty recently, so all this stuff was already running through my mind. To tell the truth, the show actually wasn't as bad as I'd remembered it being. Maybe I was more nitpicky as a kid, lol.