The Ratchet remake is the worst of the main line games.
Not disagreeing with you there.
While 3 I felt was pretty rushed, at least you can tell the people behind it wanted it to be a good game and it had some great things going for it.
The remake takes away a lot of the old charm and personality of the original series.
Sly 4 was overall a better game than Sly 3.
In terms of gameplay, I suppose it's sort of neck and neck. Both games had huge problems in terms of adding a whole bunch of extra characters and mini-games in place of interesting and well designed levels and challenges.
Although Sly 3 still had somewhat of a cohesive mission structure, in that every mission you do helps set up the final act in each chapter. Sly 4 on the other hand had no such structure. It felt like every mission you did was simply there just for the sake of it and there was very little in terms of build up. The whole thing just felt so sloppy to me. It didn't help that every mission marker was either really close to the safe house or just led to a completely different area which meant that the main areas weren't really capitalized on as much as they should have been.
In addition, every time you beat a mission you get sent straight back to the safehouse instead of going back there on your own, which discourages exploration and getting the feel of the level you're in.
Also the loading times are absolutely abhorrent. How did we go from picking a character and instantaneously going outside the safehouse to explore to picking a character, sitting through a thirty second loading screen and then leaving the safehouse?
Overall, despite sharing general design problems, Sly 3 I feel is still better in this regard. If only because the basic structure and design choices from Sly 2 are still there and it's generally better optimized.
Also, I don't even need to mention Sly 4's final boss fight. What a goddamn embarrassment that was.
Story wise, Sly 3 wins out for me there hands down. Yeah, it had some pretty glaring issues. For one, I wasn't really a fan of how you've essentially became an errand boy rather than... well a thief. It makes sense in the context of the story, but I don't think it translated well into the game. Some of the new characters were kinda hit and miss, and the whole thing with the Panda King was an interesting idea, but probably could have been handled a bit better.
I think the climax and ending though actually wrapped things up pretty nicely overall thematically and character wise for the most part.
Sly 4 however was pretty much glorified fanfiction. Characters getting flanderized or acting out of character, time travel, repeats of previously established character arcs, the main antagonist being the poor man's Clockwerk, and a shitty cliffhanger ending.
I guess the one positive thing I can say about Sly 4 is that it brought clue bottles back which were strangely absent in 3. But that's about the only thing going for it I think.