After having seen the first two, there was no reason I wouldn’t go all the way. At this point I could at least identify with Frodo and Sam on one aspect: their hardship to reach the Mordor and destroy the ring was very similar to my struggle to reach the end of this cinematic trilogy and finally remove it from my watchlist. Because there is no half-measures to be taken, I watched the extended versions of each of them, which pushes the last one to 4 hours. Those 4 hours went faster than the 7 hours of the first two opus united. It’s actually good. We get to see the origin of Gollum and the extent of his villainy. There is a super-scary bigass spider. Gandalf does some badass kung-fu with his stick when he is bored of using it for actually wizardry. The army of Rohan charges with their horses at stupid orcs on bare foot in the most epic of epic battles. Éowyn kills some high-ranked Nazgûl because she is no man, you stupid motherfucker. Then there is the big climatic conclusion in the heart of the Mordor, where you really root for Frodo to succeed because you don’t want to have spent 11 fucking hours in front of your TV watching elfs and wizards for nothing.
I’m pretty sure you could cut 45 minutes out of The Return of the King and replace them with a synthetic edition of The Fellowship of the Ring and The Two Towers. Even narratively speaking, the whole Saruman mess that is dealt with by the first two movies seems useless in comparison to the power that Sauron can yield in the last one.