How accurate is it to say that the nature of government under Lenin and Stalin was markedly different?

One of the most important things to do when answering a question like this is explain the links between your factors. You also need to establish criteria by which the question can be judged. You need to show sufficient knowledge and make sure your answer is well organised.
So, for example one general thesis to apply to this question would be that Stalin's nature of government was just a more extreme version than the one put in place by Lenin, and therefore it is not accurate as instead of being markedly different, Stalin's government was a more centralised continuation. There are a number of factors you could use to back this up, however, a good one to use would be that both leaders used extreme violence to fight real and perceived threats against their regimes eg: Lenin's red terror and Stalin's Purges. Both used similar repression methods and relied on an atmosphere of fear to facilitate their oppression however, whereas Lenin's terror had systematic targets Stalin's 1930's purge affected anyone with the smallest blight on their record. You could then link this to how both leaders increased power centralisation but Stalin created a cult of personality. As long as a clear thesis runs through your answers and you signpost keywords in the question, you should achieve top marks.