I love everything about the mounts. They make movement not only freer, but they way Anet implemented them, they each represent a different type of movement. You can not only select the right mount for the current obstacle, but also switch them while traveling to make exploration that much more enjoyable.
There is one thing for me, however, that feels a little restricted about how mounts work, and that's the fact that you cannot dismount while in mid-air. Now that we have so many tools at our disposal for getting around, I often encounter situations where I would love it if I could switch to gliding or to a different mount in mid-air, but all I can do is continue falling with my mount until we both hit the ground.
As an example, it would feel awesome to jump off a cliff with my raptor, then at the end of his leap, hop off, switch to the griffon, fly to a nearby updraft, then dismount and take out the glider to make use of the updraft.
Hope I can do that in GW2 some day.