Just from the DAO hack, you can learn a lot of things of how Ethereum works as a project and a company:
- Ethereum's design (turing completeness etc.) doesn't enable formal verification of code/contracts
- Months before the hack, Ethereum had paid for security audits, in the report the way the DAO hack was done was described, yet Ethereum failed to do anything about.
- It's up to the decision of Ethereum's corporation (a.k.a Ethereum Foundation) to decide if they don't like one transaction or contract to make a hardfork, they broke one of their selling points of code is law.
On a sidenote, the 3rd largest cryptocurrency is a instant/premined scam[1] and the 5th largest is a super-centralized system that you can barely call cryptocurrency. So marketcap doesn't prove much.