Multiplayer is extremely important. Just think of games like DOTA, Counter Strike, Call of Duty - those are all the biggest games in the world and why are they so big? Because the multiplayer is great. Games would be nowhere without it, there would be no communities, no competitiveness, no eSports and no social aspect to it. I usually finish singleplayer to get the feel and controls of the game, then I head off to multiplayer and start my journey.
Singleplayer is usually something you just play once or twice and then leave, it gets mundane. Sure, sometimes it's great to play alone, especially in games where the multiplayer community is either a bunch of hackers or a bunch of people ten times better than you, but multiplayer wins it for me.