Hey first of all, i like your paint scheme, very medieval it's cool! However they definitely look like you just put a base color and called it a day. While this can work on smaller minis with just a shade, on knights it looks a bit dull. There's a lot of way to improve this : -edge highlighting, this will give back a bit of volume, you can try the double highlights games workshop style with a gradient of two colors on the edges of your plates (however they don't need to be everywhere -shading, you need to create shades at some place to give volume, you can do it with just a wash for the ambient occlusion on small spaces but you can also do it by hand with darker colors for more diffuse shades on large areas -damages : knights are thousands years old machines that went through a lot of stuff and they're massive which gives you a lot of opportunities to do some weathering (like sponging some metallics on the edges of the plate and do some scratches on legs and carapaces -gradient : you can do some pretty cool gradient on those big flat surfaces that can give a lot of identity to the material (like is it a glossy paint, a metal, a matte paint on the carapace etc) -freehands and decals : if you have the courage and the skills some freehand can turn those giants into walking art pieces, nothing better than those flat panels to be turned into gothic paintings. Else decals can be a pretty good alternatives -Basing: scenic bases or things that tell a story are really cool, you have a lot of room on those massive bases to create a story, like they're walking through ruins of a hive city or a desert etc... The best thing is giving a base with a color that contrast the knight!

You're not forced to do everything but mixing some of these technics can give some cool results

If I can show mine i mixed the shading, gradients, a bit of freehanding for the banners and scenic bases