I liked the story of this module. I also liked the gimmick of it, to an extent, with the focus on weather as a very real hurdle to overcome.
However, the first part is so hard that my players really had trouble enjoying themselves. The weather rules could use some streamlining, and some more give. The penalty to ranged attacks was especially brutal, since many enemies in the forest flew. I did make some tweaks to make some encounters cool (playing with low visibility on Roll20 due to snow was fun). But beware: the encounters in the forest are going to be very, very hard for a level 1 party. Judging from my players' reactions, it wasn't the fun kind of hard.
Once they got out of the forest, though, it picked up. The next section was a cool town and dungeon crawl. I enjoy how alien and oppressive Irrisen feels. What really attracts me to this AP is that it's definitely not a "standard" fantasy setting. The book does a good job of making the dungeons feel otherwordly and should take players out of their comfort zone.
PROS: Does a good job of evoking a "stranger in a strange land" feeling. The second section is really nicely done, with a really neat dungeon to end the module. The story is very dark in a satisfying way-- expect your players to see terrible things happening to people in this AP. Irrisen pulls no punches, like a fairy tale if you take out all the whimsy.
CONS: Difficulty (too high for the first section). Weather mechanics can bog down gameplay, and can make some builds feel useless (like ranged attackers). If I had to run it again, I'd homebrew some stuff to get the players to level 2 before launching into this module.