Being a "sound guy" myself, I find sounds and sound system extremely important. Although realtime filters like echoes, reverbiation, and EQ'ing does indeed have value, it wouldn't be the first thing I would fix or add. Echoes isn't something I've heard a lot of in games, except some wildly configured cheap springverb. Everywhere I encounter reverbiation in games, they go completely nuts about it rather than subtle.
Some ideas about a new updated sound system:
* Check walls and propagation magnitude, not (only) 3D distance. Extremely important for indoors, For outdoors, occlusion and obstruction should be sufficient.
* Stereo files for everything. As distance increases to sound source, stereo width decreases. Fully close, stereo width is full, but only about 25% amp on the "far ear".
* Weak doppler effect.
* Resurrect Acute Hearing
Should decrease background noises (ambiance) so that chatting NPCs or approaching footsteps can be heard from farther away.
* Sound occlusion and obstruction.
* Sound maps or some kind of environmental sound type parameter depending on area. I.e. rain would sound different for: Meadows, rocks, houses, paveways/roads, lakes and sea, and maybe modulated (i.e. by EQ) by mud, ice and snow cover.
* Entering water slowly and sneaky shouldn't leave a big splash - few manages to get this correct.
* Fix the current sound problems/bugs, I'm experiencing a few...