People who don't like the band love Gore for the same reasons some people who love the band don't like Gore. I used to be a lurker here and I was appalled at all the complaining, but Gore was the first album to actually upset me. It's not a bad album, but it's the first that I actually dislike from a band I worshipped for years. I think the longer you're a fan it's just a natural thing to start complaining, it's like a long marriage. It's not new and exciting like when you first discovered it, and you actually can start to resent it, but at the end of the day you love that bitch.
I think you are right, I think for long time fans you have a level of expectation depending on when you really got hooked on the band and they will never really quite live up to that again because it will never be as fresh and new sounding as it was (like for me when I first got hooked on WP). But you still love their sound and there is no other band that can match that vibe like the deftones do so even sub-par deftones is better than most alt/metal stuff that is out there...
That being said, I think it is entirely predictable that a band will usually peak around albums 2-3 then tend to trend down... deftones have lasted far beyond that IMO (though I think most people still consider either ATF or WP their best albums)
but for me personally Gore is the first album they've done where I can really feel that digression in everything from the mix, the riffs, lyrics to point where the band felt a little stale and dated to me, which is kind of depressing.
I hope they bounce back with their next album (assuming there will be another one) but maybe Chino is spread too thin these days with his multiple project and the ideas well for deftones is running a little dry as of late or maybe not as focused on it's core sound (Stef's dissonance combined with Abe's groove) as it should be with Chino pretty much taking creative control these days.
Or maybe Chino needs to inject Chuck Doom into this project too, LOL, to help his song writing.