Ethereum's initial success can be attributed to a few elements. Ethereum is programable, meaning apps can run on the Ethereum blockchain. This is what let to Ethereum being used in:
Decentralised Finance, or DeFi, meaning that apps like investments, insurance etc can be run without a central authority.
NFTs, tokens to prove the authenticity and ownership of an object (digital or physical)
The consensus in the network through proof of stake. New coins are created by putting guaranteeing your existing money. This incentives people to be good actors and decreases the money supply, increasing its price.