Considering the main innovation within bitcoin is the fact that it solves the problem of how to get a decentralised network to agree on a certain thing, it's strange you would even ask this.
I'd say its the "thing" and the agreement to that are the innovations.
The blockchain is what solves the problem of consensus on decentralised networks. That's the innovation, everything else had already existed. So, what would be the point of having a blockchain on a centralised currency?
But the blockchain is just a ledger. So if you want to, we can say there's no innovation as everything did exist before. Peer-to-peer isn't new, decentralised banking isn't new (original banks weren't centralised). This is all a bit of an existential problem for bitcoin now... for me the key point is the mix of technologies, and the driver is the secure prevention of double-spending in an unregulated, electronic transfer mechanism - it has created
trust, that the thing. I don't believe the current decentralisation will last long, it will remain distributed, but with consolidation of mining to a small number of nodes.