Mixed bag. My first experience was with my Denon 2807 in the apartment. Audyssey made the center (VP150) sound very hollow and tinny, just unbearable. However, it seemed to make the surround sound seem more 3d, but later doing blind A/B tests I couldn’t distinguish the difference in the surround sound with Audyssey on or off. Though I could instantly tell if it was on with the VP150 in the mix. I must have run Audyssey 100 times in my apartment and it never sounded good overall.
Here in my house I got similar but not as stark results with the Denon 2807. When I switched to the Onkyo 3007 things got a little better. Audyssey did seem to “tighten” up the bass a little. Didn’t do much to the VP150 when I tried it out here, but it sounded so crappy by itself in this room it didn’t matter. Blind tests confirmed that the bass got a little better, however even with the Audyssey flat curve I can tell when it’s running with the higher frequencies because it deadens the ambience in some music. I listen to a lot of very ambient music, most regular recordings seem unaffected for the better or worse at higher frequencies.
Sorry there is no short answer as to weather is sounded better or worse right away since I ran it when I first got my speakers. Though when I did turn it off for the first time in the apartment everything suddenly sounded better. I would describe it as more lively, energetic natural sounding.
Note that I find all DSP a mixed bag. Sometimes I find it enhances material and other times not. Hard to define exactly when but generally the better the recording the less I like any DSP while the worse the recording (up to a point) the more various DSP settings help. Personally I think people should try all the settings on their equipment to see what works for them. One of my favorite is “All Channel Stereo.” Now I just need to pick up a few used M80v2s at auction if you people would just start upgrading.
Disclaimer: Yes, I know how to run Audyssey please no more links to “The Audyssey Thread.”