As much as I hate RE5 I can't place in trash tier. I like the Mercs and co-op too much for that.
Top tier:
RE2R
RE4
RE3
RE3R
RE7
REmake
RE2
Generally, these are all good. RE2R is better than RE2, but just not everywhere making the original still worthwhile to check out. RE3R is simply a completely different take on RE3, they are 2 different experiences. The roles the characters play and the outcome are the same but everything else plays out different. OG RE3 had mercs, RE3R has the same unlocks, but by replaying the main game that does change stuff once you go above Hard.
REmake for example, makes the original game redundant. Its the same game, but much nicer to look at and its expanded.
Mid tier:
CV
RE1
RE Zero
RE5
RE5 is the worst of this lot but offers the best side content and most replay value.
Trash Tier:
Revelations
Revelations 2
RE6
These games are simply awful. Revelations 2 had a nice episodic story, but in terms of gameplay, graphics and overall design its a very bad game. Especially if you play it in one go. Rev 1 is even worse, its just all around terrible. RE6 is a franken game. The developers just threw everything they could at it, and saw what sticks. Thats not an awful lot, RE6 is absolutely terrible. The gameplay would have some potential if the level design and enemy AI was designed around it. The story is insulting, even for a Resident Evil.