There are lots of reasons to read Orwell's letter, essays and journalism:
1. He's a great writer. It's a pleasure to read him, just for entertainment value. There's a little piece of doggerel from Orwell's school days that he quotes several times that is now stuck in my head:
The rain it raineth every day
Upon the just and the unjust fella
But more upon the just because
The unjust has the just's umbrella
I don't know why that sticks with me, but it's a great illustration of Orwell's use of solid, colloquial and even humorous English.
Moreover, in addition to providing wonderful model prose he occasionally writes essays about writing and language (the use of "Basic English", oratorical versus conversational English, what drives a writer, the totalitarian perversion of word meanings, etc.), which are insightful and interesting.
2. If you're interested in the Second World War (or for that matter, the Spanish Civil War), Orwell's writings amount to a sort of diary, a primary document. Even his book reviews almost inevitably contain some reference to the political and historical scene.
3. Orwell loved socialism (yes, the man who write _1984_ was a democratic socialist), but he loved freedom more. His simultaneous battle for socialism and against totalitarianism (i.e., the Soviet Union) is engaging, even -- or maybe particularly -- where he drops the ball.
I think Orwell's heart was in the right place -- he had seen close up (and written a good deal about) the suffering of the poor. Like many people who have their hearts in the right place, he jumped immediately to the idea that redistribution of private property and collective ownership of the means of production were the only way forward.
On the other hand, he was a writer and a man of ideas, a person who greatly prized personal freedom. His essays give an intriguing glimpse into the battle raging inside him between collectivism and individual liberty.
I don't have a copy in front of me as I write this, but I'm pretty sure this first volume contains Orwell's unforgettable essays on the inner life of colonialism, "Shooting an Elephant" and "A Hanging". I highly recommend this set to anyone who is the least bit interested in Orwell.