As a general rule, when you compare down jackets, you're looking at a few factors:
1. shell/liner material
2. down fill and quality)
For a recent discussion on this, check out Will's recent review of the WM Flight. In it, he compares it with MB Inner down and Skaha Plus jackets. Also take note that MB just improved the Inner down by bosting it to 2.5 oz of down, as compared to WM's 3 and Nunatak's 5.0. I'm not sure how the Alpine Light compares with previous models.