OpenSea is good for some things, but at the moment very expensive. To authorize sales you have to do a "free" one time transaction, as well as subsequently a one off transaction for each smart contract you wish to trade. After that, you can place bids and prices on NFTs for no costs, only having to sign the signatures authorizing the sale if someone else pays for the transaction. But otherwise each purchase when paying the transaction fees is quite costly.
The main advantage seems to be the ability to bid and place prices from cold storage devices, while keeping assets in your wallet (unlike CryptoKitties where you have to send them to the contract technically). As I said it's expensive, but I think getting setup is worthwhile if you want to get collecting.
Personally I just bought some MoonCats as the wrap & rescue operation sounded adorable, as well as a couple of
hashmasks so far. The opportunities of NFTs, a market worth less than $1b, seems far more inviting than altcoins right now. I still remember when DeFi was worth less than $1 billion in locked up captial

With digital art now making up 1% of global art sales, it's worth paying attention to, even if it makes up less than 0.05% of the crypto market.