Yeah, keep it as is. It'd bring all sorts of problems if you had only 4 directions and the player could only shoot in the direction they are moving (which I'd assumed from a cursory glance at the comments above), but as is with the ability to strafe and run backwards while shooting in one direction, 4 directions are plenty (although 8 would also make sense).

I have no doubt you'll design the levels to accommodate any control restrictions, as well.

Jibb