Typically, what happens is you wander through a level smacking the living crap out of a stream of orcs, goblins and spectres.
What we have, in the parlance of console gaming (ROTK is released simultaneously on PC, PS2, Xbox and GBA), is known as a free-roaming beat 'em up. From there it follows three paths - one staying with Gandalf, one tracking Aragorn, Legolas and Gimli, and the third trailing Sam and Frodo as they venture deep into Mordor. Return Of The King, as you'd expect, picks up the story with the victory at Helm's Deep.
So maybe it's to redress the balance that EA has undertaken to release such a relentlessly action-packed tie-in to round off the movie trilogy. How Many of us who've read The Lord Of The Rings can claim to not have skipped those increasingly mind-numbing transcriptions of Elvish songs? Come on, maybe you ploughed through the first couple, but be honest, it is the literary equivalent of watching paint dry.