the move from framework to core should be smooth outside of a few areas. - webforms/asp.net framework won't move over easily - windows GUI apps won't move over

the move from framework to core should be smooth outside of a few areas. - webforms/asp.net framework won't move over easily - windows GUI apps won't move over easily - some windows specific API's didn't come over (such as WPF). If your app falls into any (or multiple) of the above then you definitely would have experienced pain, but in general the move is pretty smooth.