fofig is defintiely on point with the idea of the markers limiting you, and you trying to "push and pull" from within your image, ie, setting down a tone and then working it in two directions towards shadows or highlights
also youre limited because markers come in set pallettes and set colors, your pictures turned out better colored and have a better scheme than a lot of things created under a predefined pallette, but i think this is hurting your overall progress, you dont have the challenge of creating your own tones and colors and accents and palletes, and this is one of the MAJOR aspects that will push you to the next level
i like the concepts and the choice of images, but I woudln't encourage doing a bunch of the same things, i wouldnt even encourage doing most of someones stuff on one single style
i think the main thing that all these lacks is depth in darkness, it sorta works and gives a pop art sorta feel for most, but it hurts a little bit in some areas - the picture with the two people sitting on the curb, i think this is the one that is lacking most out of the lot; theres a lot of unused area washed with the same tones of grey. be weary about using gray with no color/saturation in it, for the most part it ends up coming out bland and sorta amatuerish, experiment with adding subtle blues or purples or even reds when using selecting a grey tone, this is the type of effect that will add a lot more depth and youll find its used a lot by people on here pretty well
i like the pic with the two little girls the most, mostly because of the patterns and the thin black outline - i think your style is cool but you need to develop it more and push it in differnt directions, ie. interesting use of patterns or outlines, it really distinguishes it from the others.
keep it up post more stay productive!