First of all, despite what others have said the demo is very playable on keyboard- you just have to set up custom controls in the launcher. I'll admit though, the movement control system is literally tenky, as in you move forwards or backwards in relation to the direction you're aiming. While I do agree that it's the most technically accurate way to mimic rollerblading (at least in theory), there's a small matter of momentum and directional movement based on the tank-style. To make sense, when rollerblading in a straight line you start off with a small boost of acceleration (your first step and the push that follows), bringing you up to at least 50% of your average speed in the first few seconds. Also, when turning your forward momentum is redirected (not cancelled out for momentum in the new direction), meaning that a turn can actually speed you up depending on the angle. I think specifically it's the turning and forward/backward control style that (while I was able to get used to) would frusterate the average player.
To fix this, I recommend that the joystick (or in my case 'wasd') control not only the direction, but also the camera and forward push, and swap the now unused forward button for a 180/90 degree character rotation, both for tricks and movement tweaking. Or just "rotate right/left on the spot" buttons.
Personally I'd recommend that the camera follow behind the player and "lock on" to within 15-20 degrees, and have a seperate button you hit to unlock it (so you can look around without moving as an option, instead of the default), and a double-tap to recenter it.
Then there's the jump, which is a very typical demo-game jump. I presume it's a placeholder until you can get a sort of tap/hold -> short hop/high jumpflip system working.
Again, very playable and I had fun, even collected 4 badges before I had to start fighting the momentum and inertia. Also, I saw a few people complain that the rails are "too thin"- I can see why they'd say this, but with the tweaks to the movement system it won't be much of an issue.
I have hope for this game, and eagerly await the next demo version!