Really? I've seen the various films many times now and the first is always the more sombre, quiet one to me. Watched Evolution only a couple of hours ago too.
It may just be me, but it seemed that the sequel had less goin' on, noise & soundtrack wise than the first...
I see what you mean now, yeah the first film experimented much more visually and audibly with various filters, digital alteration, and on a smaller budget with cheaper equipment it made for a surreal backing to the film.
Evolution had one main blue visual filter and did the entire audio track normally. So it looks and sounds far "cleaner".