Octodad was today's Steam daily; game is on sale for $0.99. From my perspective, this is a type of deal Steam needs to keep doing; offer a game like Octodad for a buck. Steam does not advertise outside of Steam and may want to consider better promos and marketing if trying to drive sales.
In thinking about the various websites now that sell Steam keys, I think Fanatical has made the most improvements and learned how to use social media and marketing better than the others. They regularly have a daily deal and come out with bundles, some great, some meh.
Groupees has gone downhill but, to be fair, is the best site for music bundles. Now that their Be Mines are no longer under the sub that they prolonged delivery of, I am cautious about the quality going forward.
IG has made some improvements overall i.e. expanded their base of game offerings, have times of free games (sometimes just DRM free), but the quality of bundles have been declining.
GMG, I think has been good at evaluating the trends and learning when to simply cut the sale price in relation to Steam and Humble. The addition of GMG credit has only helped them.
Humble, well I think we can agree that IGN taking over was not helpful. The monthly is still a good value and they have been trying to promote bundles via live feeds and such. The continued decline in quality of what was the weekly bundle, and taking away any HB store credit from buying bundles, along with good competition from other sites such as GMG have made me examine my purchases more closely. Humble's book and comic bundles are good values if you like the material. I will say that audiobook bundles are more my style.
CDkeys is worth mentioning as I believe they were smart with the 3% off via Facebook like so that they can send you promos via Facebook. CDkeys is better than G2A and has been the lowest price site for games such as Doom, Gears of War 4, CoD titles.
Having said all of the above, I realize that Steam may be counting on reddit, CAG, Slickdeals, other sites that monitor prices to market for them and after all, Steam is the current King of the Hill.