Okay, it's 3D... SO the modeling is good, action is smooth... and overall (so far anyway) you've got obvious skill with the craft.
It's short... I know it's a loop and you may even intend it to be a short one, so this isn't so much a "problem" as an observation. You will grow in following and acclaim, though, by extending your loops.
ACTION... here's where you'd improve the MOST with the LEAST investment. A few more frames with her rising and falling a few more inches over the course. Don't get me wrong, this is nice... BUT we don't just want nice porn'. Do we?
We want to build from a cute start to a raunchy mid-term grind, and a pounding, pulsating, nasty finish... money-shot and all.
Audio... Not going to beat you up about it. It's silent and you've got ears... I will point out that "No audio is only better than BAD audio." SO... my advice in this category, is if and/or when you start adding audio, be careful to take as much attention on that part of the work as you do in the visual stuff.
Overall, I'm sticking to three stars. I think it's fair, and for me, it's a bit above average. Hope this helps... Don't forget to breathe, and relax a minute from time to time... then keep on keeping on. You're probably wise not to "fountain" everything you've got into uploads, too. It can make your work seem "cheap" or "easy" too quickly. Better to tease a few at a time, and then take the advice garnered to either add onto them and repost, OR to build onto others that you can return to "works in progress"... ;o)