Tartuffe's reputation precedes him. His name is the title, and the characters of this play spend all their time talking about him – but he doesn't even show up in person until Act 3. By this point, we've already heard what the rest of the characters think of him. In Act 1, Scene 1, Dorine calls him a fraud; Damis tells Madame Pernelle that his "every action makes me seethe and tremble/ With helpless anger" (1.1.24). Madame Pernelle, on the other hand, believes he's a "fine man" who "practises precisely what he preaches" (1.1.17). Orgon is similarly positive, if not quite as clear, in his praise. Tartuffe, he tells Cléante, "is a man who…a man who…an excellent man" (1.1.5).
So, by Act 3, we know how Tartuffe is perceived, and we know what kind of trouble he's been causing, but we don't know him. He hangs over the play, a mysterious, malicious, bad, bad, bad influence. As it turns out, he is, of course, a bad dude, but he's also really...well…we don't know how to put this any other way…really lame. Which is to say, he's not the kind of villain who talks in a deep Darth Vader-esque growl or uses his incredible intellect to trick his victims. He just knows how to find the feeble-minded – in this case, Orgon – and exploit them.
Now, we must admit that the whole eviction notice thing is pretty clever. However, most of what we actually see him doing on stage is pretty embarrassing. His (failed) seduction of Elmire is nothing short of pitiful. He actually tells her that he's "no angel," as if that will make her see him, a supposedly holy man, in a whole new light (3.3.29). Can you think of a cheesier line? We can't.
His fundamental lack of suavity is what makes Tartuffe a memorable character. We get to laugh at him when he tries, rather awkwardly, to put his hand on Elmire's knee and fumbles with collar of her dress. We get to snicker when we see the easily detectable hollowness of his supposed piety. If he were totally smooth and effortlessly evil, we might like him too much. As it stands, we're both amused by him, and horrified by how easily he's come to dominate Orgon. When he finally gets his just deserts, sure we cheer, but we also hope that maybe, just maybe, he's capable of turning his life around.