High Gas and Transaction Fees: Ethereum transaction fees depend on the gas market, which fluctuates depending on the usage of Ethereum. Frequent state updates on the deployed contract are expensive, and commitments must be timed to reduce costs.
High Complexity: Due to the EVM's complexity, there are multiple avenues for unexpected results. Hence a thorough audit is required before using a contract in production.
Uncertainty due to Proof of Stake shift: Since Ethereum is shifting to a PoS system in the near future, it is unclear if all functionality of Ethereum-L1 will be replicated on the new chain. It is also unclear if new smart contracts need to be developed for the PoS chain or whether the PoS chain will be backward compatible with Ethereum 1.0.