The most impressive thing for me about bitcoin is just to how much extent it can be customized, and how much easy it is to use. The simplicity alone makes it worth using. Its transactions speeds, the peer to peer validation process of the blockchain is fascinating too. The way bitcoin, or rather the blockchain tech can enhance cyber security is pretty cool.
Also, bitcoin transaction fees are configurable depending upon the urgency of the transaction, and this makes it really easy for me to send out small transactions, since thats what I do mostly.