This has been discussed a lot in some of the other areas of the forums, but those areas are sort of specialized and often the general players doesn't read them.
In my opinion however the new sounds I"ve been hearing are terrible. The gun sounds are way off and sound quite amateur. The stock gun sounds are a lot better, and a LOT more true to reality when it comes to comparing the game to real sounds the guns make. Some of the new gun sounds, like the MP40 on one sound mod are like bb guns firing too fast.
As for the grenade sound, to me it sounds like a boulder hitting a gravel pile, and nothing at all like an explosion. When you hear an explosion, you hear a concussion, not a SPLITCH sound.
Some maps have "new" background explosions/arty (Smolensk Stalemate in particular). This is by far the worst yet of all the new sounds. It is clearly a recording of someone banging on a 45 gallon drum or aluminum sheet and a smaller, gascan or large coffee tin. Again, the stock sounds are much better.
I think what happens is someone creates or transfers over from another source some sounds they personally like and having a personal investment in them they think they are good. There is NOTHING wrong with the stock sounds, in fact I think Tripwire has done a fantastic job with the quality of the sounds. All these sound mods are just a backwards detriment to realism and immersion.