Nice to meet yah Gregor. Anyway thought I'd give you some opinions (I say opinions because I'm a noob myself)
Anyway first thing I notice about this is that your tiles have a larger saturation than your knight. Due to this the tiles pop a lot more than your character, causing the eye to fly straight past the knight.
Your new cave walls definitely look better however the rocks bland in with the roof part of the walls, add some more blue to the tops and slight yellow tint the rocks, aka move them slightly in opposite directions of the hue wheel thing.
As for your grass you need to try and break away from the grid, aka not perfectly square as you have it. See how your cave base turns, try something similar to that with your grass.
As for the original walls, I kind of see upside down picket fences. Unfortunately that distracts me from giving any real C&C on that.
ps see how you have that purple colour ramp, 3rd wall map, trying doing something along those lines for the knights armour to make him more notice-able.
Hey, well opinions still matter

Yeah the tiles do pop out a bit too much, I cut down on the saturation on the tiles now and make them blend in more.
You're right, they do blend in too much, I've fiddled with it a bit as you'll see below, I need to make it darker though (or make the knight brighter) because the knights blend in too much right now.
Redone the walls now, made it more brick-like and less like just long lines of rock.
I'll see what I can do about the grass, not entirely sure on how much (or if) I'll use it, if I plan on using it a lot I'm definietly going to do what you said and stay away from the grid. Thanks for the help!

Edit : Updated so that the knight is brighter, I have also started working on an alternative stance.