There’s a lot of content to play as a free player. For me the most important thing the subscription offers is the unlimited crafting material bag. You don’t need it but if you want to be a crafter it will be painful without it. Three classes and bunch of content is behind expansion packs… all of which you can unlock by buying the current “collection” version which includes all the previous expansions also and goes for like 60 bucks…

If you enjoy ESO then the free version is a trap as buying the ESO + expansions pack is much cheaper than buying all the expansions.
You don’t need the expansions to try out the game, nor a sub.

AFAIK, you can play the base game for free, no subscription needed. That said, there is a subscription that buys you a better user experience, and once you run out of content you’ll have to purchase the expansions.