2046 is loose sequel of 'In the Mood for Love'. Both are from same director and have same lead actor. Both have beautiful music and many more similarities.
2046 is the sequel of In the Mood for Love. Both explore love and loss, and change of feelings overtime. You don't really need to watch in chronological order as each can be viewed as a separate.
Both are beautiful, sensual and aesthetic movies that were both directed by Wong Kar Wai. Both also seem like character studies of the female lead where the male lead takes more of an observer role (2046 explores the male main lead more). The romance stays unfullfilled as well. Gong Li acts in both.