So, lemme preface this by saying that after playing many-a-game with cotdp, generally speaking I do like the expansion. The encoutners are unique, exhibit items are fun, spells are cool, not bad for a 'small box'.
There is, however, one thing that pisses me off about it pretty much every game. It seems to have a lot of encounters/mythos cards in which you have to search the monster cup for monster X and put it into play/fight it, etc. This is really superbly annoying. It completely disrupts the flow of play as I search through piles of monsters looking for a mi-goh, a ghost, a maniac, a hound of tindalos, etc. This has been done before (DH expansion with Brown Jerkin encounter at the witch house) and afterwards (Innsmouth Look search for a deep one...), but not quite to the *extent* that it seems to be a problem in Cotdp.
It seriously drives me crazy. Every time I practically have to empty the whole monster cup in some space that apparently the game designers think you have available on your table after setting up this space-intensive game, which means that this usually takes place on my lap. I have to worry about losing/dropping monster chits, not to mention finding the right ones in the first place. Worse still, there are a few cards that summon *all* the monsters of one type, Ghosts/maniacs in "Escape from Arkham Asylum" and "Meuseum Haunted". Then you have to go through the cup and find not one, but two or three of the things. Only once you've gotten every single one can you go back to your game. It breaks the tension of the game and it's extremely frusterating.
To a point that I'm considering making proxy monster trophies to 'stand-in' for the real ones, then if in the event that monster is drawn from the cup the regular way, an investigator with a proxy trophy could take the real monster as a trophy and then redraw the monster that is supposed to come out. I think I might do this. It's the only way I can dull my rage.