The first meeting with a major villain should be a memorable event.

To achieve this, you need to lay some groundwork. Mention the villain's name well in advance of any expectation of any meeting with the PCs. Build up the villain's reputation with rumours and hearsay. Let the PCs hear tales of some of the horrible things the villain has done. Let them see the gruesome aftermath of some of the villain's activities. Have the PCs encounter low-level minions of the villain, carrying out part of what appears to be some secret master plan. Let them realise slowly just how horrible that master plan is, and how powerless they appear to be to stop it.

Then when they meet this criminal mastermind have it be on the villain's terms. Have the PCs be helpless to do anything but listen and, perhaps, talk.

Then have the villain say something that they never expected and which totally blows their minds away. It barely matters what it actually is; it can be almost anything. The main requirements are just that it's dramatic and unexpected.

Transcript

Obi-Wan: ... setting traps even as he was invading the ship. Clearly this General Grievous is methodical and effective.
Anakin: He may be a bigger threat than Dookû.
Obi-Wan: With Dookû dead, the Separatists will need a new "leader". I wonder—
General Grievous: You fools! It shall be I!
Anakin: General Grievous, I assume?
General Grievous: Little wormlings.
Obi-Wan: What are you planning to do with your army of droids?
General Grievous: Droids? Droids?
General Grievous: Tut tut, you bore me.
General Grievous: Inside each exists the mind of a sapient being.
General Grievous: The finest brains harvested from across the Galaxy.
General Grievous: No mere droids, my poor deluded child. They are cyborgs.
General Grievous: Cyborgs.
General Grievous: Under.
General Grievous: My.
General Grievous: Command!