I think A:M is a good animation program. Fairly optimized and easy to use, IMHO. The patch modeling takes a little getting used to if you're coming from another program (like Maya), but you do learn to appreciate the easy-of-use and flexibility of patches. They're fairly similar to NURBS without some of the funkiness. I actually wish Maya had A:M's patches.
Rigging in A:M is a breeze. Fast, easy, and it works. Not quite to the technical nitty-gritty of Maya's rigging features, but they work just fine. In fact, I originally learned how to rig and animate characters with A:M. It was pretty easy to learn.
I'm not really a big fan of the interface, but people seem to like it. Too many floating windows and not enough customization allowed. Maybe I'm just too particular in my work habits.
Overall, it's not a bad program to learn. Unfortunately, it has a reputation of being a hobbyist's tool and isn't used a lot in mainstream production. It's also a program that is constantly being patched and updated, which is a good and bad thing. Good in that bugs are fixed regularly. Bad in that you have to do a ton of updates on a regular basis, and, as with many software updates, new bugs have a tendency to show up regularly. For the price, though, you really can't complain too much.