It's an excellent addition to a superb game. Snow and dynamite add just enough to make it feel different from the base game, while still retaining all the familiar aspects. The only downside is that it reduces the game to a four-player maximum; a five-player group with a love of Snowdonia might find that frustrating. [EDIT: Sorry, that's just the Jungfrau scenario – Mount Washington still goes to 5 players!]
I prefer the Jungfrau scenario to Mount Washington, partially because I'm not that keen on the Devil's Shingle mechanism in the latter (miss a station spot and you're hosed for Surveyor points), but probably mainly because I've been to the Jungfrau region several times and know the area well.
my games will be limited to 2P so i am not concerned.