C2 is awesome, but coming from actionscript events based programming with large teams of developers, I find that these are my biggest challenges:
1) no user defined events.
E.g. there are about 20 places I want to say end the game for various different reasons and do a load of house keeping and display stuff, i.e.I want to raise an event called "gameEnded" with some parameters, and have one event handler defined. Importing event sheets goes part way to solving this, but is more like a "goto". Also, the concept of change listeners would be nice, so if say the score changed, this could trigger some actions.
2) no way to re-use code. I re-type a lot of code in a lot of games which are all similar to each other. This is a bit of a maintenance nightmare - when I change the common "library" code, I will have to edit 30+ games, and retest them all in case I made the C2 equivalent of a typo. You dont seem to be able to cut and paste actions between projects, even if you call the objects the same names. I experimented with manually editing the event sheets in notepad++, but kept crashing C2 (not surprisingly).
There is a function plugin someone wrote, but as a general rule we don't touch plugins if they are not part of the supported C2 product so may end up not being maintained, bug fixed or working with a release.