Not at all. Sure, if you can make a game that has a great Single Player experience as well as a good Multi Player experience, more power to you. However, if that Single Player experience suffers because of the time spent producing the Multi Player experience, there's something wrong. Basically, I can break my favourites down to three categories.
Single Player emphasis: Playing good games from this category is almost like watching a good movie, or reading a good novel. The story and scenes stick with you for a while. They can have multi-player, but it is not necessary to get a great experience from the game. (Examples: CoD 4, Oblivion)
Multi Player emphasis: Good games here know they are multi-player games and really emphasize it. There could be a story, but it's really not necessary. Besides, what could be better than randomly dropping you into a server with 19 other people just to try to shoot each other down? (Example: Battlefield 1942)
Merged Single and Multi Player: These games play well in both Single and Multi Player, and typically play the same in both. Being able to seamlessly go between Single and Multi Player is a bonus. (Examples: Street Fighter, Rock Band 2)
A bit lengthy, but I think it gets the job done.