I just bought a couple items in the store a few minutes ago, and when I went to download them, it's telling me I have 1873 items to download. I just formatted my hard drive about a month (or so) ago and re installed everything from scratch at that time, including store items through GG, at least what it told me it needed to download. It was tens of GBs and took most of a day(actually, longer, now that I think about it). It is not possible for me to know if it downloaded everything at that time, of course. I've also since received the latest DLC. Was there some massive update to content that has transpired in the past month or so?
Desktop: i7 4770@3.4Ghz, 12GB RAM, Win 10/64, GeForce GTX 1080, 1TB SSD, 1TB HDD; Laptop: i7 4800MQ@2.7Ghz, 16GB RAM, Win 10/64, GeForce GTX870M , 1TB SSD.