korell: I managed to find a demo version of Catacomb 3D so that I could try out the controls, and now I can see what you mean. However, I find the keyboard turning to be a bit off for a first person perspective. For instance, with keyboard turning you get a constant rate of turn speed, whilst with the mouse you can turn slowly or quickly, which is more intuituve and gives a feeling of greater control.
I have a utility (a DOS application that runs in DOSBox) that cancels mouse forward and backward motion. I used this for Blake Stone and Wolfenstein 3D, so I can try running it with that to stop the mouse moving me forwards and backwards.
Then I'll try using the DOSBox keymapper to adjust the controls. The cursor keys (turn left and right, move forwards and backwards) and the keypad (for combinations of turning and moving) are okay, but they are quite distant from the other controls (H, B, N for heal, bolt and nuke, as well as the numbers for the scrolls). I could try using the keymapper for W and S for cursor up and down, and A and D for the strafe modifier plus left and right cursor, so that they are strafe left and right. This is similar to what I did for Blake Stone and Wolfenstein, giving a more modern control feel, but it doesn't give strafe turning as the modifier causes mouse left and right to strafe too, but it is still something.
UPDATE:
It worked fine, and upping the mouse sensitivity in the DOSBox config file (to 150 instead of 100) also improved the mouselook.
So now my controls are:
Mouse for left and right turning
Mouse left click - fire
W - forwards
S - backwards
A - strafe left
D - strafe right
Shift - run (both shift keys activate run)
H - healing potion
B - rapid fire bolt
N - nuke blast
And the following controls still exist for optional usage:
Mouse right click - strafe
Ctrl - fire
Alt - strafe
Cursor keys for forwards, backwards and turning
Keypad controls for movement and turning combinations
The only downside is that the WSAD keys are dual mapped to both the letters themselves (for typing savegame and highscore names) aswell as the cursor keys (with the strafe modifier for A and D), but this only causes a minor irritation when typing the letters in a name as sometimes the cursor moves either before or after typing those particular letters.
As mentioned before, though, you still can't strafe and turn at the same time as the modifier activates meaning mouse turning becomes strafing too, but then the game was never designed for strafe turning anyway, so it isn't a flaw as such.
Can you please post a tutorial on how to change the controls? And the name of the application that unbinds the mouse y-axis?