I like every gen and have actively enjoyed each, and these are my honest opinions
These do not take into account FRLG/HGSS

>Region
6>4>3>1>2>5

>Set of new Pokemon
1>5>6>2>3>4

>Gyms
1>3>5>6>4>2

>General NPC Trainers
6>4>3>2>5>1

>Music
3>1>2>4>6>5

Story
5>4>1>6=2=3

Starters
1>5>6>2>3>4

Legendaries
5>2>6>1>3>4

Postgame
2>4>5>6>3>1 6 has potential to move up with free DLC though

I was going to make a metagame and graphics part but those go straight 6>5>4>3>2>1