1) Crowns! (Haven't cashed out yet, but it's good to know I already can.)
2) Wagering cubits - it's not about ratings anymore.
3) The concept of sit'n'go tournaments.
4) The concept of warzone tournaments - non-stop action, rewarding faster play.
5) All in all the best casual chess server around - has many important features (pre-move, auto-queen, lag compensation, anti-cheating measures, etc.) that really separate the good chess servers from the bad.
1) The execution of warzone tournaments. The single biggest gripe is the imbalanced points handicap system. It's ridiculous how as of now it's much more rewarding to play at the 1800 level rather than 2300, for example. All it does is alienating stronger players. When the idea is to encourage players of all levels to participate in the same tournament, a much better solution is separate prize categories restricted to players within certain rating ranges.
2) Tournament cancellation. Why sit'n'go tournaments are ever cancelled is beyond me. After all, the idea is for a tournament to automatically start when enough players gather, whenever they gather. Also, even though the situation has improved as of late, it's worth mentioning how annoying it was to wait a few days for some big tournament, only to see it cancelled despite over 20 rather strong players showing up. Another tournament related issue is the inability to withdraw from a tournament.
3) The auto-seek system could always use more flexibility. As of now only the rating parameter is somewhat flexible. Sometimes I have to wait a few minutes before someone accepts a rather specific "rated, 1-minute, 500 cubits, ±300 ratings range" challenge from me, when in reality I'd happily auto-accept any "rated, 1-5 minutes, no increment, >100 cubits, ±300 ratings range" challenge, for example.
4) Ratings system. Bullet, blitz and slow ratings should be separated. On the contrary, there isn't a reason whatsoever for a separate tournament rating.
5) Clumsy design of game database and statistics - mainly the lack of search capabilities whatsoever. Also, there isn't enough variety and detail in the stats.