This is sorta related to the small principle in visual design, that you shouldn't actually make rounded corners by joining a straight line (of infinite radius) to an arc of a fixed radius—because things don't work that way in nature. Instead, the radius should change gradually in and out.
If only Arrow Dynamics understood that when they designed their roller coasters. Maybe they'd still be in business instead of losing to B&M and Intamin.
AD seem to have been able to make the pitch flow quite alright, but dropped the ball on the roll movement. Shame—the ride per se looks exciting just from the vid.
The other problem Arrow had was the lack of heartlining. That is, the axis of rotation when banking.
For optimum comfort of the rider, when the track banks, the center of rotation should be at the rider's chest. Arrow fails to do this, and places the center of rotation between the rails. This causes any banking to create a significant lateral force on the rider, which whips the rider's head into the over-the-shoulder retraint. In a proper heartlined roll, the track appears to "slip" from under the train, like this: [0]
In the video I linked, the turnaround after the two vertical loops was particularly brutal and painful.
What makes it even worse is a poor design of the wheel assemblies. The wheels on the inside of the rail that keep the car centered are designed to allow a small gap between them and the rail, and they're not spring-loaded or dampened in any way, which causes extreme levels of hunting oscillations [0].
Their roller coaster Drachen Fire [1][2] was so rough and painful that they stopping running the ride out after only 6 years.
