Building suspense?

Very quickly...

I would have used deeper, darker sounds overall. The floor creaks accompanying the footsteps is one example.

Less score, more atmosphere to make the setting more dangerous.

Some breathing from the "hunter" would add some tension.

The "controller" needs some computer sounds, perhaps just keyboard/mousing sounds; his space sounds empty and dead. It also needs to contrast and sound "safe".

I really disliked the Mickey Mouse scoring at approx. 1:00.

The heartbeat was incredibly cliché.

Chair needs to creak when "controller" leans back.

I thought that the ending of the ray-gun sound effects were really corny.

Not bad, but I'd agree with less score. One thing I thought of was the shot of the footsteps. For some reason it occurred to me that the shot might be scarier looking if the camera shot the footsteps from a front shot of them, rather than diagonal. But maybe that's just me, and it wouldn't have an effect on anyone else...