I played Autumn as well. Now, my group was VERY much the wrong group for this adventure, so, it didn't go over all that well.
It works a lot better if you let it grow more organically - don't force stuff. Let the players wander around, poking into the various bits and bobs in Waterdeep for a while and try to make the city actually matter. But, again, you need a lot of player buy in here.
There are a TON of extra resources on DM's Guild now as well that will really, really flesh things out.
BTW, the whole 1/4 of the material gets used is not really fair. You actually use almost all of the adventure. The first three chapters are the same regardless of season. Once you hit chapter 4 and the plot thickens, so to speak, all the seasons use the same encounters, just with minor variations and a different order. And the conclusion will be the same regardless of season.
But, I do agree with
@Lyxen here that to make this adventure really pop, you should sit down and do a LOT of work. This module does not work particularly well out of the box. At least, it didn't for me. Then again, in my group, after spending two or three sessions getting the mansion, dealing with repairing it and making it theirs, the only feedback I got was that the mansion is close to a sewer access.
Totally took all the wind out of my sails and frankly, I did skip over more than a few encounters to just get the thing over with.
My advice to anyone running this is to make ABSOLUTELY sure everyone is bought into it. If you've got a Kick-in-the-Door group that isn't really interested in setting or plot, this module will be terrible to play.