Originally Posted by
JudicatorPrime
There are some powers that are specific to Mjolnir, like absorbing, amplifying and expelling energy of any kind; flight; teleportation; time travel; creating force fields; etc. Some writers have also intimated that Thor can't expel his godforce energies without the hammer. Other writers still have indicated that Thor has a greater degree of control of elemental forces with the hammer. It's not that he can't summon lightning or rain, but he wouldn't be able to control it with the same degree of precision as he does with Mjolnir in hand. I'll let you all decide whether or not that's complete b/s. As is typically the case, different writers spin Thor's (and Mjolnir's) powers differently.
At the end of the day, though, Odin's primary enchantment on Mjolnir is that it bestows all of Thor's inherent abilities in addition to the powers that Mjolnir contains onto anyone who wins the hammer. Considering how powerful Thor is, that makes it a highly desirable ball-peen, despite the Arthurian sword and stone stipulation of "worthiness" attached.