Are you asking about current winter driving conditions or the general condition of the highway? I can't tell you about current snow conditions, as they change daily and hourly, but have driven it when it was partly snow covered twice. Once, I drove from the turnoff at Watson Lake all the way to Deese Lake making first tracks in the snow. That trek took me all the daylight hours just to make that short distance. In general, the road is in very good shape. It is paved the entire length - except for a short segment on the south side of the Stikine River. In many places it is narrow and winding and built up without guard rails so it does require some care in driving and is not a high speed route. It is about 100 miles shorter than the Alcan but requires more time to make the shorter distance. It traverses some fantastically beautiful scenery but I have never seen the numbers or variety of wildlife one normally sees on the Alcan. I enjoy driving both highways and make the round trip once each year.
You can not go wrong running the Cassier. That is now my preferred route in the summer. Last summer there was only about a 5 mile stretch that was dirt. My nice white toy hauler did not pickup mud till we hit the ALCAN. Early, late, or winter season travel can be tough as snow plowing is not a high priority. Late winter season avalanches can be an issue. Last thing is you need to be able to go at least 350 miles between fuel stops and I still would recommend carrying enough fuel to get you another 100 miles. Go the Cassier for the ride not to save time.
Last enjoy the trip. The scenery, wildlife and people along the road are spectacular. The wooden bridges are nicier to cross then the concrete counterparts elsewhere in the world. My Wife and I rode our motorcycles for a good portion of the highway while our daughter followed behind us with the truck and trailer (yes we did rotate who got stuck in the truck). Also would recommend a side trip into Hyder....nothing specific just another one of the unique places in Alaska to visit. Personally now I have been as far north, south, and west that you can drive in Alaska