Mostly everything works okay with Cinnamon 2.4.
However, there are some problems to know about before updating.
First, it seems to break the configurable menu applet. It sometimes takes two or three tries to open some programs from the menu. The default menu works fine, but just this configurable menu applet seems to have been broken. It also disables the ability to add apps to the panel for some reason and all right click functions have a considerable 3 or 4 second delay. Adding to favorites works, but not adding to panel. The main problem is the unresponsive clicking though. If you hate the default menu and use configurable menu this is probably the worst thing about updating.
(other applets seem to work fine, though).
Also, the new themes window is practically useless, even if it has some good ideas in theory. As almost all themes for windows and controls are just previewed as grey rectangles. The window itself has so much wasted space to the right and below previews. Also, no icon previews except the folders.