If you don't want spoilers, don't read this. However, this excerpt (no horrible spoilers, I think) sums up my reaction to the worst part of the film:
VICINITY OF CIRITH UNGOL
GOLLUM: Dead hobbitses...(mutter mutter)...won't be long now...(mutter mutter)...will try wearing Ring on toe this time; yes, precious; very beautiful...
SAM: Hey! I heard that!
FRODO: Heard what?
GOLLUM: Nothing, Master! Fat hobbit wants Ring; yes, Master.
SAM: I do not!
FRODO: I think maybe you do. Gollum wouldn't lie to me, after all.
SAM: He's trying to kill us! We're walking straight into a trap. I'm not going one step further.
FRODO: Leave, then. I'm sick of your paranoid delusions anyhow.
SAM: But I...
FRODO: Go on - get out of here. Good riddance.
SAM: But you...
FRODO: Have a nice death.
FRODO stomps off. SAM stays behind, weeping piteously.
PEOPLE WHO HAVE READ THE BOOK: ...the f**k??
CREEPY CAVE
FRODO gets tangled in a gigantic spider-web.
FRODO: Egads! Does this mean a gigantic spider lives here?
GOLLUM: Ha ha! Smeagol tricked you, ssstupid hobbit! Did Master know "gullible" was not in dictionary?
FRODO: Oh, dear. Maybe it wasn't such a good idea to send Sam away.
AUDIENCE: Duh!
SHELOB appears and starts pounding down the tunnel. FRODO lights up the star-glass and gives us an all-too-clear look at her.
ARACHNOPHOBES IN AUDIENCE: Oh...dear...God.
FRODO cuts himself loose and runs like hell - but, being FRODO, falls down. GOLLUM jumps on him.
GOLLUM: Jussst kidding about "ssstupid" comment! Nice master! Hold still so spider can eat you, yes yes.
FRODO: I have a different plan, actually.
FRODO flings GOLLUM down an abyss.
PEOPLE WHO HAVE THE BOOK: You know, it's interesting: even though I've read the book, I have no idea what's going on.