Lord V. doesn't make his first appearance until the movie is like 90% done, but he definitely makes a splash when he does finally show up.
We mean that literally. He only comes to life after Wormtail dumps him in a cauldron with a few choice (read: gross) ingredients, including Harry's blood. Yeech.
Of course, he's been able to make mischief for the entire film using just his minions Wormtail and Barty Crouch Junior. Through their assistance, he rigs the Triwizard Tournament so Harry enters (and wins) and is then transported to a graveyard where Voldemort can steal his blood. Oh, and he manages to kill a couple of other people along the way as well.
And yeah, he got all that done before he was fully alive again. Are you getting now why people have been so afraid of his coming back? Imagine all the damage he can do with a fully functioning body.
The minute he's all whole again, Voldemort has one big item on his agenda: kill Harry Potter. However, because he's a combo of sadist and drama queen, he can't just go ahead do that right away. No—first, he has to assemble all of his former pals to him and then give them hell about how they abandoned him back when he first lost his body:
VOLDEMORT: Welcome, my friends. Thirteen years it's been, and yet, here you stand before me as though it were only yesterday. I confess myself disappointed. Not one of you tried to find me. Crabbe! Macnair! Goyle! Not even you, Lucius.
LUCIUS MALFOY: My Lord, had I detected any sign, a whisper of your whereabouts…
VOLDEMORT: There were signs, my slippery friend. And more than whispers.
Voldemort has made his point clear: his friends suck, and they should probably be feeling pretty scared right about now given that the Dark Lord thinks they have been disloyal.
Voldemort quickly shifts focus back to Harry, though. He's got an audience now, so he's ready to dispose of Harry once and for all.
Now, you'd think that the easiest way to do this, if you're Voldemort, would be just to keep Harry immobilized by magic and send the killing curse his way. Raise your hand: who thinks Voldy took this option?
That's right: He sure didn't. Instead, he insists that he and Harry duel.
VOLDEMORT: Pick up your wand, Potter. I said pick it up! Get up! Get up! You've been taught how to duel, l presume, yes? First, we bow to each other. Come on, now, Harry, the niceties must be observed. Dumbledore wouldn't want you
to forget your manners, would he? I said bow. That's better. And now…
VOLDEMORT: Crucio! Crucio! Attaboy, Harry. Your parents would be proud. Especially your filthy Muggle mother.
HARRY: Expelliar—[Voldemort deflects the spell.]
VOLDEMORT: I'm going to kill you, Harry Potter. I'm going to destroy you. After tonight, no one will ever again question my powers. After tonight, if they speak of you they'll speak only of how you begged for death. And I, being a merciful Lord obliged.
We're guessing that Voldemort really took the whole "Harry being immune to his magic/powers when he was just a baby" thing pretty hard—why else would he need to prove that he can "beat" Harry?
And, of course, he can't. Voldemort's theatrics end with Harry's wand locked in battle with Voldemort's, and then Harry breaking the bond and escaping before Voldemort can kill him.
Just goes to show you: pride will get you every time. Voldemort is definitely full of it, and his attempts to win some kind of symbolic battle with Harry end up with his prey getting away. He may be a very clever wizard, but in this case, his ego managed to get in the way of his goal of disposing of his archenemy.
For now, anyway.