A few of the unique things I try to emphasize when talking about Lit because it's so different from a framework:
Lit is just helpers to make web components. It's implementation detail. On the outside the components are just standard HTML elements.
Because of that, Lit makes no assumption that other elements you're using in your components are made with Lit. This low coupling preserves interop, and makes it easy to incrementally adopt Lit, and incrementally leave it if you wish. Low lock-in is an important principle for us.
Because of the low coupling, Lit doesn't have any centralized scheduling, diffing, etc. Each component is its own independent render root and schedules its own updates in microtasks. This has some great upsides - it's very easy to modify scheduling per component, and decouple costly subsections of a page to limit jank.
And we get great performance from the emergent global properties of independent roots. We check for data changes in the property setters for each component, so data updates only cause component updates along the paths in the tree that both use that data and see a change. Then lit-html, the template system, doesn't use VDOM, but remembers where data is bound to the DOM and only updates that if the data changed. It's very efficient.
Also, Lit requires no compiler to toolchain. You can use it from a CDN, or with import maps, or with a tool that resolves JS modules import specifiers. You can use decorators with TypeScript, or not. You can bundle or not. We do have TypeScript and ESLint plugins for working with templates.