Initially we wanted the plane to just lean over as a visual indicator when you were turning (not fully roll), but a bug made in the execution made it so the plane would lean when your pressed left, and rolled furiously when you pressed right. The bug added a lot of added challenge, because you could then only yaw left and roll left, and was crazy-fun as hell. We really considered keeping it, but it was dramatically motion-sickness inducing, it also made our physics overhaul do crazy things like rolling the plane would make gravity go up. Figuring out what we were doing wrong to get leaning stabilized was taking too long, so we cut the whole idea of leaning the plane and later found another cool visual indicator as the smoke billowed behind the plane at high speeds.
The other bug was that the terrain which worked well in downloadable Unity builds freaks out in WebGL (it's just too big). We kept it in both because one mate worked hard on it, and people have mostly looked past the buggy-terrain for the fun gameplay.