This one strays a bit more from the books. When Fellowship differed from the books, it was generally because Peter Jackson had to leave stuff out. In Two Towers, he seems to be putting stuff in. By and large, it's perfectly okay, because the added bits resonate with other scenes... in short, the tweaks make sense, from a movie perspective.

Elves at Helm's Deep. There's several reasons for this anomaly. It adds a little physical weight against the long-standing Tolkien complaint that all these powerful elves never do anything over the course of the story. The Professor can explain it over many chapters; all PJ can do is some rushed scenes with elves talking about Valinor. In the movie's vision, the elves battalion also helps bolster Theoden's defense... PJ's version of the defense of Helm's Deep is more hopeless than Tolkien's, in my opinion. The women and children stuck in the Glittering Caves, the six hours notice of the impending attack... and no huorns to bail everybody out at the end. But I think the most important reason is the return of Haldir. If PJ was doing a straight translation of the book, we'd have tons and tons of characters that are introduced, do something fairly important, and then never seen again. Haldir is a recognizable character from Fellowship, part of the movie's supporting cast... and he returns in Two Towers to die. It's actually kind of nice to see somebody important die. Nothing truly terrible ever happens to our leads - which is why Aragorn was tossed over a cliff - so B-teamers like Haldir (and Hama) have to step up.

Faramir. I have to admit I was a little bothered by this darker Faramir, but then I read this article from The One Ring.net which puts it into perspective. The movie version doesn't seem so off now. In the book, he just had more stage time to develop his interrogation and come to his decision. And "A chance for Faramir, Captain of Gondor, to show his quality" is one of my favorite lines. The battle scenes in Osgiliath are added just so all three storylines can culminate in war.

The truncated Entmoot. Much too hasty. I thought this was one of the weaker drifts, simply because it's purpose is to reveal an overwrought environmentalist moment. Treebeard really should have been aware of the deforestation of Isengard, and not be tricked by Merry and Pippen into discovering it. Still, I'd rather have a slightly dopey Treebeard than no Treebeard at all. The payoff for the altered Ent scenes is the inclusion of the amazing attack on Isengard, a portion that Tolkien totally glosses over. Maybe Return of the King will begin with Gandalf and company riding to Isengard and finding Merry and Pippen at their ease among the ruin.