I'm only playing through the main series games on the PC. I haven't touched the spin-offs even though at least a few of them are probably more legit than the main games.
So far I'd say RE4 is far and away my favorite, with 7 and the remake of 2 following behind. 5 was a straight up mess of a game, 1 is a product of a different time, and 0 is a less successful attempt a re-creating 1.
6 falls right in the middle, but I'd say it's night and day better than 5. Some of the plots feel repetitious (aka. everyone has an invincible nemesis that keeps showing up), but it's a fun thrill ride.
There are a lot of rumors going around about a new game that may or may not be RE8 coming next year. Per those reports, it will continue following Ethan and Chris from RE7, but will be set in the Carpathian region. Enemies are said to include lycanthropes and mythical monsters. All of those things sound up my alley, so I'm definitely okay with that. I know RE4 was set Spain, but I think it's pretty clear it was originally intended to be that area, too.
Out of curiosity, did you play the original RE1/DC, or REMake? Because I still love the Gamecube Remake of 1. I agree on most of the other points.
As for the spinoffs, they basically suck, though Gaiden on the GBC is interesting. Revelations was a hot mess, and I'm honestly not expecting much from Revelations 2. You can see the point where Capcom tried to go back to "classic" RE after 5, but botched the implementation (Revelations).