I've been to Sky Valley twice now, both times the day after a big dump of snow. Once was nice and sunny, the other snowing with nil to little visibility. Both times it was a great resort to be at.
The base at Sky Valley is situated in a very narrow valley, to reach the lower lifts you have to walk though the base building. It's a two story building bottom floor has two changing rooms (male and female), rental area, shop and toilets. Upper floor has ticket office, small cafe, and more toilets. Once though the building there are two double lifts that take you up to the resort area proper. at the end of the day you have a choice of coming back down these lifts, or skiing/boarding down a narrow, and at times steep trail. I wouldn't recommend this trail for beginners. If you are a beginner it might be better to go to Hyperbowl. Both resorts share a lift ticket and for all intends and purposes are the same resort.
Once up the lift to the main ski area there is a choice of lifts one double, one triple. the double takes you over to the boundary with Hyperbowl, and gives you access to the resturants, a two different runs back to the bottom of the lift, and the entrance to the trail back to the main base.
The triple takes you straight up the mountain giving access to the same areas as the double, but also allowing you to head across to the bottom of the last lift. This lift will get you to the top of the mountain. the triple also enables you to head over to Hyperbowl, and gives access to two different "park" areas with all the usual play things for boarders, along with a half pipe. SnowJapan info shows that the split between skiers and boarders is 20/80 (although on the days I was there i think it was more likely 5/95). So boarders are well catered for.
There are three different restaurants on the hill, the largest (and only one open on week days) is number three. They all serve a good selection of food, along with all the drink vending machines. The cafe at the base also does good food, especially the curry rice.
It appears most of the people who go here (at least on the days I was there) prefer the groomed areas to the powder. On both days (admittedly both a day after a big dump) there was untouched powder right up till the resort shut.
The top half of the resort has a number of areas that those of a more adventurous bent could easily dive into, I saw a number of possible runs though trees and into some very deep untouched powder that wouldn't have meant ducking ropes.
The only downside to Sky Valley is the complete lack of facilities for kids, especially kids who aren't skiing or boarding. I also wouldn't recommend it for non skiing/boarding adults. There is no way to get to the main restaurant (number 3) without a set of skis or a board.
As the resort shares a ticket with Hyperbowl, and is only separated by a rope in a couple of places, as long as you make sure you get back to the Sky Valley side by the time the lifts close you can treat them as one resort. Therefore instead of a resort with 5 lifts and 8 courses you are actually at a resort with 9 lifts and 17 courses. All the more reason to visit.
I've been there twice, and would go again if in Osaka and had the chance to go skiing.
No specific date.
Snow condition on visit:
Things I liked:
Good snow, nice runs, especially if combining with Hyperbowl, no piped music
Things I didn't like:
Parking charges, makes an expensive day if by yourself