I measure the success of bitcoin a number of ways.  I think first off the health of the blockchain is always the most important factor.  If things aren't running smoothly, no one is going to want to use bitcoin.  I think public adoption in any ways also greatly measures the success of bitcoin.  What companies are adding it to thier accepted payment forms?  Which companies are adopting blockchain and using bitcoin for certain dealings.  What government regulations have been a positive for bitcoin and other cryptocurrencies etc.