I feel like you have hit this wall in the past. And while us here do look forward to your work, it is not the only thing that defines you. But if you lament it as your loss, perhaps it is time to do some soul searching and inspiration seeking. While you wait your turn to speak, you have plenty of opportunity to listen.

If you're not feeling it, experience suggests the best thing to do - if you're me, at any rate - is to put it down and let it lie a while. Don't feel guilty about not touching it, and take the break gladly. Enjoy the time you'd spend cringing and fretting at the thought of picking it up by doing something you'd enjoy more at that moment.

If it comes back to you? All the better. But don't let it concern you until you miss it, if that moment should arrive.

Personally, I enjoy your work. You've got a style all your own and I love seeing sketches and those broad, open landscapes you'd paint. I think it's fair to say there's marked improvement over the last decade, so not knowing where to go might feel totally natural.

Switch up your game? Maybe it's time to drop NSFW (if even just temporary) and find some new content you yourself can appreciate making mixed in with studies to improve.
Maybe you need to find a new medium as well.

If I had to give any advice, - and I'm mostly mirroring what the previous two people have said here - I'd say try to mix things up, see what else interests you that works. Try something new, draw subject matter you otherwise don't (but are still comfortable with the idea of, obviously) or characters you haven't drawn before and failing that... it may help to take a break from things altogether for a while! Simply don't concern yourself with art at all for a while, think about other things, then come back to it when you feel the vibe once more, work away any obstacles if you need to.

You've definitely been improving over time, even if you don't see it it yourself!

Draw me grinder porn.

If you're not feeling the current style and still wanna be creative, change mediums! Try some 3D stuff. Make some game levels. Do some video stuff.

2D animation? Your style seems like it'd be good for that.

Zbrush

Changing media might be an option as others have said, but my suggestion would be, if you've reached the apex of how you show, perhaps you should now focus on the message you tell with your work. Is there a story you've ever wanted to illustrate but didn't because at the time you didn't think you could do it justice?

Do what feels best. There's no point in banging your head against a metaphorical wall out of a sense of obligation. The next thing to come, if there is one, should arise naturally. If you feel you're done, whether for a time or for all time, that's entirely your decision. I (and the rest of the nerds hereabouts) would certainly enjoy further works, but anyone who says that their needs vis-à-vis art consumption supersede the the needs of the creator is a creep who should be discarded.

Try Webchemy. It's something like those ink blot tests and it's really good at jump starting your creativity. That and you can save your works as vectors:

http://webchemy.org/

There's also a symmetry feature as well.