Is probably becouse it has reflections for pretty much all water surfaces which few games and they are not Crysis nor U2. Both those lack in parts or use cubemaps to fake reflections (Crysis only ocean has full reflections, limited for rivers). Funny becouse Far Cry 1 had reflections on all water surfaces and reflected everything.
EDIT: Anyway if for Warhead you're talking about the tunnel or cave then it has distortion for sub surface objects/terrain. Just enable the flashlight or shot down the roof lights and pick them up and use em as flashlights to see! ^^
Anyway I find Anno1404 to have more impressive water than Crysis and others not just becouse it is highly detailed deformable 3D water mesh far into horisontbeing physics based with refractions, HQ shader effects, very high res reflections, sub surface rendering with caustics and more. Impressed me a lot. I actually have a dev video about their water implementation. ^^
Close view.
http://img51.imageshack.us/img51/378/anno14045.jpg
http://img64.imageshack.us/img64/6844/anno14041.jpg
http://img197.imageshack.us/img197/8171/anno1404.jpg
Water high view overview.
http://img197.imageshack.us/img197/4026/anno14043.jpg
http://img41.imageshack.us/img41/8499/anno14044.jpg
http://img196.imageshack.us/img196/9969/anno14046.jpg