Hi, thanks for your kind comment. Actually, WASD is not used to move forward, instead just moves up/down/left/right perpendicular to your movement direction, so you can reach the walls of the tunnel. (note, there's still a bug, left/right are exchanged when looking backwards).
The forward movement within the scene happens at a fixed speed of blood flow and you only can accelerate by pressing the spacebar (costs energy) or by reaching the speed proteins. For this, you need to used WASD to get near the wall, where they reside.
You are right, high speed makes it really difficult. So sometimes better skip speed proteins. You also can slow down with right mouse button. but be careful not to run out of time. All in all, it's sometimes even better to run through at highest speed without shooting any virus at all, just to collect energy and get more time extension on each round, sometimes it even can be better to slow down to shoot more viruses. It's a balance though, and to get the highest score you even might decide to take many rounds to kill all phagocytes as well, but watch time remaining...
After all viruses are killed, the next level starts, but that does not yet exist...
There's still a lot to improve. Thank you very much for your kind comment.