Earendil - so? If the empire wasn't able to survive his death (regardless of the why), doesn't that sort of mean he failed to plan ahead, which is sort of a weakness when it comes to being called "great ruler"?
It's impossible to plan ahead for a major disaster the like of an earthquake or a plague. It is, however, very possible to make plans ahead of time for your death. A ruler who fails to do so does not deserve the title of "great ruler".
Plus, what has Alexander done that Qin Shi Huangdi did not achieve? Carve out a sizeable empire? Yes, they both did that (China might have been smaller, but OTOH most of Alexander's empire was the already-existing Persian empire, which Alexander took by force the throne to - and without having to fight all that much for it) . Attempt to bring some unity to the empire? They both did that - Qin Shi Huangdi by unifying their measures and monetary system, Alexander through attempted cultural integration. Great building project? Yes, they both did that. Alexander built any number of cities to his own glory (Alexandria this and Alexandria that), and Shi Huangdi had a wall built - the first incarnation of the famous "Wonder of the World #8" - The Great Wall of China.
So, in the end, what can we compare them over? How much land each conquered? Not a very fair comparison system, that - when you get right down to it, what did Alexander accomplish with the Persian Empire that, say, William the Conqueror didn't accomplish with England - or the later Qing dynasty in China.
QSH built himself an empire. Alexander stole himself one. QSH's empire lasted some while, and in fact its latest incarnation still exists today as a world power. Alexander's didn't, and Macedonia today is pretty much an European backwater. I don't know about you, but I know which of these two I would consider the greater ruler.