ashecitism
Member
https://medium.com/steam-spy/steam-sales-in-2015-2e81a6bb0f5a#.d0hazfirp
more at the link
update:
He wrote about the Winter Sale: https://medium.com/steam-spy/about-steam-winter-sale-76a75abe152a#.hed54rn8q
The 2015 was the best year for Steam yet.
It brought over 3000 new games (compared to 1900 in 2014), increased the number of concurrent users on Steam from 8M to 12M and helped over 350 million paid games find new owners.
The number of monthly releases on Steam stopped growing
Remember the graph with growing number of monthly releases on Steam that scared every indie? Well, this number stopped growing.
Indiepocalypse is cancelled, you can stop worrying now.
Paid Steam games market was worth over $3.5B in 2015
Not every dollar is going through Valve though, as some developers are selling their Steam games off Steam. And remember — this figure doesn’t include free-to-play titles or DLC! PC worldwide core games market is estimated to be around $27B in 2015 (Newzoo). So, including Dota 2 and Team Fortress 2 revenue, Valve is controlling around 15% of it. Pretty impressive!

more at the link
update:
He wrote about the Winter Sale: https://medium.com/steam-spy/about-steam-winter-sale-76a75abe152a#.hed54rn8q
At least 46 million copies of games found their new owners during Steam Winter Sale. And that only includes games that sold over 1,000 copies, because smaller changes are barely detectable by Steam Spy. That’s 50% more compared to Steam Summer Sale.
If we assume that all of those games were sold on Steam (it’s probably not the case because of bundles and third-party stores) and account for regional pricing, we can conclude that Steam Winter Sale brought at least $270M in revenue.
That’s almost twice as much as Steam Summer Sale did.