There is an online briefing and test on the airport website -
Engadin Airport St. Moritz Airlines: News. It's for jet and multi-engined turboprop operators but it doesn't do any harm doing it. As for the weather, take a look on the same website at their two webcams. When it's nice (and they reckon on 280 days of sunshine a year) it's gorgeous - last time I saw a sky as blue as you get there was Greenland!
If the weather is bad, and you're not familiar - go somewhere else. On a clear day it's easy. With scattered cloud it's still doable so long as the vis is good and the holes in the clouds are big enough to drop through. In poor vis and low cloud - forget it. You have to stay aware of where you are in relation to both the adjacent mountains and the valley floor - there a couple of protusions that could catch you out.
And when you get there, especially in winter, don't leave any drinks in the aircraft overnight. Ms16 produces really good ice lollies
The other thing is when it's busy they park stuff up to and including Citation size on the grass area west of the 03 threshold - which isn't grass but graded snow on top of ice. It feels weird to taxy on but not impossible.