Several of Lenin's most famous works: 'Imperialism, the Highest Stage of Capitalism'; 'What is to be Done?'; 'The April Theses'; and 'State and Revolution'* were written prior to the October Revolution so I would say it would be incorrect to say that Lenin's only contribution to Marxist theory were his tactics devised from his experiences post-revolution. All Marxist theory, ultimately, is of a philosophy of action, it's theory that should be attempted to be put into practice - hence Marx's 'philosophers have thus far... etc'. So Lenin is unique when compared to many Marxists in that he could test his theories in the face of the practical material conditions of revolutionary Russia. I don't think anyone should take the actions of the Bolsheviks and the theories of Lenin as some blueprint to be followed without criticism, or whatever, but you can't deny their importance in revealing some of the struggles of revolution and the problems that could arise in certain conditions - so basically I would say, if you want to understand revolution, read Lenin.
[*] one of my favourite aspects of State and Revolution is his postscript: "This pamphlet was written in August and September 1917. I had already drawn up the plan for the next, the seventh chapter, "The Experience of the Russian Revolutions of 1905 and 1917". Apart from the title, however, I had no time to write a single line of the chapter; I was "interrupted" by a political crisis--the eve of the October revolution of 1917. Such an "interruption" can only be welcomed; but the writing of the second part of this pamphlet ("The Experience of the Russian Revolutions of 1905 and 1917") will probably have to be put off for a long time. It is more pleasant and useful to go through the "experience of revolution" than to write about it".