* Payments cannot be reversed
* Users are anonymous
Advantages.
* The fixed supply created the expectation of fabulous gains that turned it into a speculative pyramid schema
* That "ponzification" in turn resulted in extremely volatile price, that makes a bad currency.
* The block reward and the market price were too high, leading to a hypertrophied and unsustainable mining industry.
* For that reason, the cost per transaction is way too high.
Fair enough. Satoshi was not prescient. I think he made it clear that he had hoped for slow, steady growth. What he got instead was massive early attention and a bubble. Bitcoin is not unique in that regard, however. So I think we should try to lay responsibility for "ponzification" of real assets (nay, the entire economy) at the feet of those actually responsible.
* Mining got inevitably centralized (last time I checked, the top 5 Chinese miners had 60% of the hashpower).
Hmm... I think this is a bit controversial. Mining centralization hasn't seemed to have had any ill effects, so far. But fair point.
* There is no mechanism to reward the relay nodes, which carry increasing load.
Premature optimization is the root of all evil.
* Its design cannot support 1 billion users, maybe not even 10 million, even indirectly.
That's actually just not true. There's good reason to believe it could support 1 billion users, indirectly at least.