For example, Feral druids are like rogues without sap and vanish and Guardian druids are like warrior tanks with half of the abilities and less mobility.
The disadvantages of the druid class are any of the abilities listed in this thread that druids don't have. Not going to restate them all here, just read up.
And if you're not convinced, I guess you'd better switch to your druid alt right away. No hyperbole.