Stayed for more than a week. My fiancee and I booked a family room for extra space, it was more spacious than I thought and great even though we were only two! The building is rustic, but very clean, and the shared kitchen was perfect for making a quick lunch or snack.
For dinner we mostly went to the restaurant/bar by the reception - it's a slim menu but everything was delicious, tasted homemade, and the staff were all so attentive and terrific!
It's about 20 minute to town, near enough for an easy walk and far enough to feel like you get away a bit.
All in all, we both loved our stay at CMC and I highly recommend you book it for your stay in Longyearbyen!