A good question and one that's been asked before. I'm of the opinion that revolution was an historical inevitability that could only have been avoided had Nicholas acquiesced to a major decentralization of power and a reduction of his own absolute authority. The First World War hastened the downfall of the semi-autocracy (which is what it was, in effect, post-1906). But such a regime ruling over a vast and diverse country such as Russia was destined for extinction within a decade or two of 1917 regardless if a devastating global war had take place or not.
What is more unfortunate is the eventual loss of the White Army to the Reds and Kerensky's downfall that allowed the Boldheviks to secure power. The post-revolution period between March-November, 1917 was Russia's opportunity at responsible western-style democracy. The war combined with radical elements within and, to be honest, an immature population known for impetuous behavior made this inpossible.
Back to Alexander II. Yes his liberation of the serfs didn't exactly make them free from total bondage and in many cases they were no better than indentured servants. This was probably a contributing factor to the dissatisfaction of the peasant population. But I think it has more to do with basic human nature at play. Give people an inch and they'll take a yard, and rightly so in many cases. One generation might have been satisfied with Alexander's reforms, but a generation or two later, under Nicholas, wanted more.
The obvious comparison that comes to mind is the abolition of slavery in the United States - also having taken place under a much revered leader (Lincoln). Perhaps the initially freed generation of former-slaves (the younger ones at least) realized that emancipation didn't equal equality they turned their attention from the issue of slavery to enfranchisement, and equal pay, and civil rights and, later, affirmative action...Reform rarely happens quickly enough for most people and it's successive generation wants more - and is often willing to fight for more - than it's predecessors.