IMO no he is not overrated at all. His influences upon music is profound esp in regards to heavy metal and hard rock. Its very possible he created the first rap music. He influenced Miles Davis a great deal. We can role threw a few more people he clearly influenced Prince, Rick James, Lenny Kravitz, Ben Harper, U2, Eddy VH, John Frusciante, David Bowie, Robert Smith (Cure), Lemmy, Queen, Steve Vai. That's just the tip.
He seems sloppy sometimes in his playing, but I think even for Jimi innovation has its difficulties. If you're the first one to go in a direction there is no clear path and exploration means wandering.
He certainly was unconventional. In fact he seemed to light convention ablaze whenever he could. People can argue that the showmanship undermined his artistic standing, but it also profoundly influenced later musical performance. Considering its long standing replication and success id say it was pure marketing genius. Whatever it was I bet Jimi would have looked down his guitar neck at any criticism.. chuckling to himself as he ate out that strat to a bell ringing climax.
Given his musical career was only like half a decade and ended at the ripe old age of 27 I wonder what those years would have brought.