It's definitely a much simpler react-like library. You don't get the React ecosystem though. If you're looking to step out beyond React, inferno is also worth considering. It focuses on performance rather than bundle size (it's smaller than React, but bigger than Preact).

> You don't get the React ecosystem though.

Well this is an odd thing to say, as there's a whole dedicated compatibility layer. That's not to say it's 100%; relying on specifics of synthetic events, such as bubbling through portals, for example, won't work but it's a drop-in replacement for many users.

Take a peek at https://preactjs.com/guide/v10/switching-to-preact/