Tomorrow has the same two actresses, Kim Hee Sun & Kim Hae Sook they both work well together in both series. Room No. 9 is about a soul switching event that changes the lives of both of the actresses. Tomorrow is about grim reapers saving souls. both have their sci-fi elements but Room No. 9 is limited in it's science fiction but it plays out pretty good.

I'm sure if you enjoyed one you'll enjoy the other.