I'm almost finished my first run through (using a keyboard, which works great for me) and it's amazing.  As a BIG fan of the original I was also a little bit apprehensive, but it does the original justice and then some.  To answer your question directly, it actually improves on the atmosphere of the first game.  The pacing, balance between exploraton, puzzle solving and combat, as well as the visuals and sounds are all spot on.  It basically feels like the original was sucked into some sort of time vortex and spit out as a modern game.  I highly recommend it.