Talking about being the King of ICO, yes, ETH is the ICO which gave over 50000% returns for the initial ICO investors, talking about the tech, ETH enabled a lot many project to successfully host there ICOs on ETH netwrok via smart contracts and hence enabled them to launch there own cryptocurrencies
Technology is not the only thing that makes ETH the best platform for ICO. I think ETH launched its first smart contract, and it was well received by startups and investors with good support tools. Recombine it better than other ICO platforms such as QTum, Stellar, NEM, NEO, ...