So, obviously coming from your background working with GMOD, you have quite the background with composition, posture/action, and light/color, but it's also quite clear that you have a ways to go before you've successfully seated yourself amongst the realm of pro digital painters (which- full disclosure- I am certainly not, so feel free to take my advice with a grain of salt).
First and foremost I must address, if by any chance you were using GMod poses to trace/reference- just keep in mind you are only stunting your growth as an artist. The more work you make yourself do, the stronger and faster your skillset will grow, and the more you use crutches to ease your work, the harder you will find it to break free of them should you find yourself trying to move past it.
NOW WITH THAT SAID-
Again you exhibit a great deal of experience with many of the elements that make a good work of art- tangible action, motion, energy, solid composition, and a commendable attempt at light and color where most painters at your experience level would be falling flat.
The first thing you can work on improving is your brush strokes. While you certainly retain an eye for detail, the key aspect to making a natural looking digital art paint is to use the largest brushes possible. It will take your work from looking chalky and plastic to natural and wholesome. There are plenty of tutorials out there you can check, and being as I know you are a facepunch member, I'd whole-heartedly advise you stop by their 'creative work that doesn't deserve a thread' for some great advice within your own community.
A few specific tips- avoid trying to paint individual strands of hair, instead look at representing the form of the hair as a whole. For skin, using the largest brushes possible is going to smooth out the texture and give you less plastic-like, chiseled features, similar with clothes. For small details using fine brushes is fine- such as the details on the Scar L, but even then the main values of the object can and should be blocked in with larger brushes.
Next is color- while it's great that you're taking massive, ambitious strides towards digipaint, one thing that you may find immensely helpful is doing some study in black and white only- this will help you find a firm foothold with values (dark vs. light) in the realm of digital brush strokes. As is your colors are looking rather flat and one dimensional, although your values themselves are above average and certainly good for someone who hasn't been doing this for years.
I think the most important thing is just to make sure that you are studying and practicing specific skills, instead of just trying to make piece after piece and hoping your skills fall in place along the way. I find with art that, generally, the less 'fun' you're having, the more beneficial the skills will be for you. Of course, it's important to find a healthy balance between fun work and hard work, but it's not healthy to only go about eating dessert and skip the important nutrients
Also, a last note, just a minor niggle- on the ScarL you have a few inaccuracies. Pay close attention to the shape of the upper receiver and how it curves, and the separation between the gas black and the body of the weapon. Always try to use reference images when painting a real world object, as that attention to detail is going to be important in setting yourself apart from the rest of the pack if you have big ambitions with the digital art path.