The biggest problem by far with this system is how many more pages you have to load to view what you want to browse. In the old system you could fine tune every field before having to load a new page. Now if I want to view mods from one specific game initially, then decide I want to search for mods for a different game or all games, I have to load several more pages to do that. In the old system I just scrolled through a drop down menu and that was done. It slows everything down.
Also, I currently am not having too much difficulty with this, but flat design inherently makes user efficiency suffer. Without signifiers indicating what is interactive such as 3d effects, shadows, and embossing, users have trouble finding what they are looking for. I hope that the design team recognize that some users may have trouble with this new design in that regard.
On thing I do appreciate immensely is not forcing a memory-gobbling infinite scroll system on us. That is always a terrible idea (looking at you, tumblr mobile app).
EDIT: I forgot to mention, when browsing, sometimes the site jumps to the last page in the results list instead of the first.
Also, the search options bar is very oversized, and I don't really like hiding it behind a foldout menu. I greatly prefer the old search options as they were off to the side, yet always visible at a glance. They also didn't take up so much space.