Check out Football Outsiders' "Four Downs: NFC North." Ryan Wilson writes that the Vikings need to add WRs this season, which I completely agree with (though I don't agree with the suggestion that Sidney Rice didn't pose a deep threat: he only had 31 catches, and those included 40 yard and 60 yard touchdown catches. His modest 12.8 yards per catch was, I think, more a reflection of the weak and generally short passing attack than his own inability to threaten deep). He also notes potential needs at defensive end and safety.
The theme continues: the Vikings are solid in most areas, but need to improve the pass defense and need to add quality components to the pass offense.