Mascarpone is what cream cheese would be if it didn't have all that gum and gunk added to it.
If you made Tiramisu without the Mascarpone, you would surely miss it.
Most Italian cheesecakes in my experience are made with ricotta! Who has a recipe for one with Mascarpone instead?
and here's an interesting tidbit... I participated in a blind mascarpone tasting once long ago in Boston.... If you've never tasted the "Polenghi" brand, I'm here to say it is head and shoulders better than all the other brands. I realize you often have to buy what you can find, but if you CAN find this, you'll be glad. as well, always be sure you are buying containers with current date listing on them!