We really enjoyed our stay, it was the highlight of our trip. The room was clean and was very spacious. Breakfast and dinner was amazing and more than what we expected. Hot spring facility was good, with lots of disposable samples to use, water was the right temperature and you can still watch the snow fall from inside if you didn't go to the outside pool.
It's a true ski in and ski out hotel, we find it very convenient, and you can ski until 8.30pm with your all day ski pass. Getting there was easy too, our bus drop us off from Chitose airport directly to hotel door and picked us up from hotel and dropped us back to Sapporo station when we leave.
We would definitely stay at Niseko Northern resort Annupuri again.