I really like the vast majority of the dex, and if I don't love one of the mons I can at least appreciate its design, there's honestly only a handful in gen 7's dex that I actively dislike.
Just going by dex order:
>Rowlet
Cute owl
>Decidueye
Cool owl
>Litten/Torracat
Basic fire cats, I like the simplicity of it and how Litten looks annoyed constantly.
>Popplio
Cute seal
>Pikipek line
Solid tropical regional bird, these guys are always cool
>Oricorio
Neat birds that are fun to use and look at, they're a well done dancing mon that makes sense
>Rockruff
Cute and determined puppy, floppy ears, 10/10
>Lycanrocs
A kickass take on split evos leading to a werewolf theme. I love all three forms and they're still one of my top favorites, although I wish Dusk had more inspiration from Midnight to make it really seem like a mix of the two, they're a cool mon, especially in the anime, but could they have at least given them new animations?
>Wishiwashi
I think they were having fun with different forms this gen, the school of fish thing they had going on was fun and creative
>Salandit/Salazzle
Poison/Fire is incredibly fun to play with, sleek lizards are neat.
>Wimpod/Golisopod
Scared little bug that runs away constantly, turns into a fucking beast at fighting if you care for it enough and believe in it. They're fantastic and Guzma owning one really tells a lot about his character in a subtle way.
>Type: Null/Silvally
I love this dude, it's a shame they never became as popular as a bunch of other mons from this generation, and I don't know why, they're a chimera, it's hard to not be cool with that theme. Playing the game and seeing Gladion bring this dude out with no context actually made me go "what the fuck?" in a Pokemon game, which was a fun experience.
I like a lot more of the mons than this, these guys are just the ones that came to mind off the top of my head and I don't want to create a massive wall of text more than I already have.