The environmental sounds in the single player levels are much improved from the previous (no-monsters) version (better balanced and more natural sounding). However, I'm not hearing the shield recharge sound (it's either absent or very quiet). It just makes other sounds quieter when it's recharging.
This is on an Athlon PC (Win98/DX8) w/SoundBlaster Live.
There are also a few things with the Pfhor models that I'm not liking as much--it's harder to tell their colors, for one thing. Truthfully, I really liked the really solid, saturated colors used for enemies in Marathon. They won't look exactly the same of course, and I don't want to ask for them to be totally monochromatic, but right now they seem a bit too indistinct in their coloring.
Also, the Spht seem a bit bright under their cloaks. They were always so mysterious, and clearly seeing their "innards" is sort of disappointing.
(But this is quibbling, I know it's a ton of work to do these models and skins and overall they're great--especially for something free.)
I also miss the look of the fists in Marathon. The brass knuckles made the idea of a killer punch more convincing, and I'm not sure how much having the hands move around all the time adds to the feel. You are a cyborg, right?
And I also saw a weird platform behavior in Blaspheme Quarantine (in the room with only three Spht in it). At one point it looked like the continually cycling platform just disappeared (dropped instantly to its lowest point), then suddenly appeared at the top of its range again. I only noticed this once though.
Overall, GREAT JOB!!! I very much look forward to seeing more!