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* The protocol has many defects that make it unsuitable or uncompetitive for the applications that have been (retroactively) proposed for it.  For example, the bounded supply led to expectations of astronomical value increases,  which induced extreme hoarding of the coin, which made its speculative price rise to 100x its utilitarian value, which caused mining to become 100x more expensive than it should be, which meant 15$ cost per transaction, ... Also, I do not consider the "pay to script" feature worth the complexity that it adds to the blockchain.  The cost structure is such that it invites spamming of the blockchain with bogus transactions and messages that have nothing to do with its payment function.   The distributed organization limits its response time.  The block reward should decrease gradually, instead of being abruptly cut by half every 4 years.  The transaction fees should perhaps be required from the start.   The organization of the ledger as a linear chain means very long 'sync' times for low-end clients. And many more.  These flaws are not fatal, because they do not invalidate the goal stated in the white paper, and could be fixed in a new iteration.  But they cannot all be fixed now in the current blockchain.
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The design supports a tremendous variety of possible transaction types that I designed years ago.  Escrow transactions, bonded contracts, third party arbitration, multi-party signature, etc.  If Bitcoin catches on in a big way, these are things we'll want to explore in the future, but they all had to be designed at the beginning to make sure they would be possible later.