Hi -- and welcome to discuss cooking!
Mascarpone cheese has a very similar texture as cream cheese, but is definitely a little smoother.
In terms of taste, mascarpone is pretty different. At its creamiest, it will taste like thick, cream-cheese-textured whipping cream. It will be buttery, rich, but also fresh tasting. Some fresh mascarpones can have a slight tang to them, but it's very subtle.
Cream cheese is a lot more sour than mascarpone.
If you need to use something in a pinch, cream cheese plus some sugar can be substituted, but it will be different. Depending on your tastes, it might be better. Generally, though, mascarpone is considered a higher-end ingredient and some people really care. Others don't, however.
Does this make sense? Really, you should get some and give it a try! Figure out if you think there's a significant difference.