Well, for the human it might work, but have you ever tried this in a game where you control a flying creature that moves in three dimensions instead of just two? How will you fly up and down?
Yes, 'I of the Dragon'. Page Up and Page Down (IIRC) changed your elevation, while clicking anywhere on the ground would have your character fly there at the current height. Most of the time you did not need to move in 3 dimensions at the same time, though there were a couple creatures who's attacks could only be avoided if you turned hard while either climbing or diving.
I usually used the keyboard to control flying, though, rather than point and click. There was no isometric camera angle; between 1st person, 3rd person and a following camera, I found the latter worked best (the 3rd person camera did not automatically turn with your dragon). With the following camera, though, you may have to change the angle higher to be able to click accurately on the ground somewhere, each time you wanted to change direction (no click and hold to direct your dragon's movement). I found it easier to just use the arrow keys, which gave better control over movement (and with the following camera provided a more visceral experience).
While keyboard controls worked great for flying, where you only need forward/stop and left/right to be able to move and hit another key to attack (with an auto-targeting system), it doesn't necessarily work well for finer control (at least not for someone who doesn't play FPS games). I've played a couple adventure games where movement was keyboard controlled and facing the right direction to talk to someone, etc, could be a pain.
You have not described combat yet, but even with just the character movement I think I would find a gamepad probably had better control and would be easier on my hands/wrists.
