I think it looks quite good, especially for something that involved such a learning curve. I'm particularly fond of how you did the mountains. They look dramatic, very mountain-ey, but they don't clash or obscure any elements of the map. I do have some critique:
Since it looks like you're not trying to stick to a monochrome palette, I think you should add some hue difference between the forests and the mountain shadows. Where you have forests near mountains, they look more like another mountain range rather than forests. I'd recommend making the mountains a little more towards blue-grey, just enough to make them clearly distinct from the forests.
Many of the labels are hard to read. The cursive typeface is partly to blame, but some of your non-cursive labels are hard to read too, because they are on too dark a background. The smaller text on forests is almost invisible, and even some of the text on the darker areas of the plains are a little hard to read (e.g. Mutant Rats). Lightening the whole map a bit would help, but if you want to keep the overall darkish look, try adding a light glow around the text, or making the text light instead of dark. I think a glow would create better contrast, but light text would allow you to create contrast without obscuring detail. See which works better for you.
"Seabreeze Plains" is stretched out too much for its length and for its typeface. One additional reason non-cursive typefaces are preferable for maps is that they can have their letters positioned separately to create a curve without distorting the letters, since they're not connected. With cursive, distorting the letters is the only way to go. In Photoshop specifically, I'm assuming you're using the text warp tool? That's very handy for most curves, since text curvature should be kept small on maps for legibility. But for when you really need a dramatic curve, I recommend putting the text on a path instead (if you google "photoshop text on a path", you'll find many tutorials). Putting text on a path rotates each letter to fit the path without distorting it. I do not recommend using it for your gentler curves, because that little bit of distortion that warping adds helps maintain the optical cohesiveness of the text. Use it only for the more extreme curves (above 45% or so), or for text with very large spacing (where the letters are too far away for the inter-letter relationships to matter much), such as what you might use for region and country names. In any case, I think "Seabreeze Plains" specifically would've been fine with a lesser curvature, there's plenty of room there.
Your rivers are disconnected from your lakes and the ocean by the black continent borders. Erase the borders in those parts. If you're trying to do this in a non-destructive fashion, consider adding a layer where you draw just the deltas without any layer effects, overlapping those borders. This could allow you to blend the rivers nicely into the lakes/ocean, too.
(Matter of taste warning) I think it would look better if the rivers tapered at their headwaters. This should be trivial to do with a tablet. Even though the rivers would probably not be visible on this scale and are thick for visibility, it's not unusual for the thickness on the map to be proportional to their actual size/volume (or at least importance). Tapering would simply be an aesthetically pleasing way to show that those rivers don't start off as grand as they are as their mouths.
A couple of more things about your rivers, they don't feel natural:
The rivers all undulate very regularly, but the undulation is too great to look symbolic. Regular-looking waving like this happens with real rivers on large scales (up close, e.g. an aerial photo), but on smaller scales (e.g. regional scale), there's usually too much terrain variation to allow for such regular patterns. Many cartographers will add a regular waving to their rivers when they don't know the detailed paths of those rivers, but this will usually be a small undulation, not something that suggests that it's the river's actual course. If you're trying to represent the rivers' actual paths (but smoothed, I presume), I would add more variation, more curves, rather than just an undulating straight line.
Several of your rivers split into multiple quite a ways off before draining into the ocean/lakes. Rivers tend to join, and it's very rare that they split naturally without rejoining for such long distances. It looks rather odd to me to have so many permanent bifurcations of major rivers.