You asked for one thing per person. I speak with the voices of three, so I’ll give you three problems
The most horrifying design flaw is how it handles on mobile devices. A couple of my professors have tried to play here, but due to limitations on their computers, they’re confined to tablets and phones to get in a good game. The problem is, the number of ways the game breaks when the site is accessed from a mobile platform has driven them from the site completely. When I went to access an sgf in the library on the website to review with friends, I nearly tossed in the towel as well. I ended up having to guess every move for one side, because only one side’s moves would show up. Occasionally, I’d get a quarter of a stone to appear. Sometimes notifications would force the whole of everything to re-size ungracefully. Further, if the phone switched aspect ratios, all hell broke loose on both the board and the layout.
Regardless of platform, I’ve had overlapping UI issues with the notification menu and the friends list. They can’t be open at the same time, and one must be manually closed to facilitate the other. Small complaint, and nothing to leave the site over. It still adds to a list, though. Two fixes exist: Have the menus give each other space, or have one close the other and visa versa when opened. Others have already elaborated enough on the overlap issues with PMs.
Outside of the layout, I can say that I’ve been frustrated more than once with games that I expected would last endlessly breaking down and losing to time. I say the game lost to time because neither I nor my opponent were happy that it ended in those cases. Most of my correspondence games have this flaw. It looks like only two have managed to be made successfully perpetual.
Finally, I suppose my biggest issue is the site’s continues breakdown when using Chrome. I’m not sure why this is happening, but I can on occasion see queries instead of player-lists. It becomes impossible to create games or challenge others to games. Somehow, I can still accept them. It’s annoying to say the least. I hate opening other browsers when I can avoid it, so I tend to just leave when those errors kick up after clearing cookies and cache. Sometimes it reoccurs in days. Sometimes it reoccurs in minutes. I have no idea what the trigger is.
The three problems: Mobile platform is broken, UI overlapping is annoying, and the site’s instability on Chrome is problematic. Of these, the first and last are the most tantalizing, and the first and second, like the second, overlap.
While none of these issues are prone to making me leave the site permanently, some have caused me to disappear for a week or so at a time. I also have to mention that those professors have left the site, and they have no intent to return unless those issues are rectified. As far as donations go, I don’t have much money to spare, so unless all of these issues are resolved, I can’t justify any expense towards the site. It’d be worthwhile to have a single place to consolidate all of my games, and that can’t be done if these issues are causing friends to quit the server.
Apologies for the long-winded response.