So, I have also bought Gotham City Impostors and The Binding of Isaac so far during the sale.
Gotham City Impostors can be really fun, but you have to make sure you have friends to play with to get the most out of it. Otherwise, the low amount of people that play this game can make things frustrating when you're up against people who play constantly which, until this sale, was almost everyone who was left playing(according to my friends who had this game earlier than me). Luckily right now there are many new players and it's a good chance to get past the learning curve if you're planning on ever getting into this game.
The Binding of Isaac has turned out to be an extremely fun game to my surprise. I have already put 14 hours into it. It has unlimited replayability due to the randomness of the levels each time you play and is overall just a lot of fun. The Wrath of the Lamb DLC is a must if you buy this game because it adds so much to the base game including over 100 new items, new levels, new bosses, and more which makes the game just a blast to play over and over again.