Known to many Russians as 'The Last Great Tsar', the final judgment on Alexander II must be that although some reform was achieved during his reign, it wasn't of such a nature that it would save The Romanovs and Tsarism when the revolution came in 1917.
He did indeed liberate the serfs, finally, in 1861, but towards the end of his life he became paranoid, and more conservative, as various factions threatened revolution and assassination. For all his caution he was assassinated in 1881. This paved the way for repression under his son and grandson, the last two Romanovs, Alexander III and Nicholas II; both of whom were present at Alexander's death.
The assassination ironically occurred on the very day on which the Tsar sought to make constitutional changes which were desperately required if the dynasty was to survive.
Alexander's reign saw relations with Britain improve in the aftermath of The Crimean War, although the Tsar himself failed fully to learn lessons from British Constitutional arrangements.
In the final analysis the question which hangs in the air is one of 'what might have been' rather than 'what was'.