Oh boy, where do I start. First and foremost. Nice job on the characters, and more importantly, there expressions. Without this element, this drawing wouldnt be what it is. Though to me twilight looks a little awkward, but thats just me.
Second, tbe shading is very nice. Im always a fan oc good shading technique, manily because im trying to find one myself
But the thing that I like the most is the textures: it gives this drawing the feel it gives off. A warm, steamy feeling that would otherwise be absent. The rock wall in the back actually looks like rock. Why im so fascinated by it, I don't know. But thats good.
(Not entirely sure about Applejack and her carefully held towel: the PONY WHY U SUDDENLY HAVE BODY ISSUES thing is amusing, but also a bit distractingly "off" in a "friends having a rollicking good time" scene rather than, sa,y a "saucy ponies" scene. But I nitpick)
This is awesome! I love their expressions in that they are clearly having a good time. Applejack with a towel despite them being nude almost all the time and Pinkie with the shark toy as if she's a kid in a bath tub adds humor to this as well. The rocky wall in the back I have to point out because it looks very nice! I know it's just rock and all... but it's just so well done.
The only thing that looks a tad off about this is the steam in places. For instance, you can see on Fluttershy's and Pinkie's mane and above them the same kind of texture in the steam and it looks kind of odd. That texture is fine for stuff like rocks, but steam is far too misty. But yet it seems to be done on purpose as it's selective where that kind of steam is, but I don't get it. Unless it's steam on glass... But that doesn't look like the kind of place setting up a glass water barrier would be necessary. Overall though that is just a minor gripe in this beautiful piece!