A move must fit all of the following criteria to be "brilliant":
- It must be the best move possible.
- It must be a sacrifice (not necessarily forced) that has very easy compensation.
- It must be at least somewhat unintuitive (at least to the average player).
- It must look like a blunder (or unnecessary) to someone who has virtually no knowledge of chess.
- It must put your opponent in Zugzwang (or otherwise leave them with no good move).
That's all there is to it.
The knight sacrifice is brilliant. !!