Going from systems like Alias and Icem into Dassaults System Catia, you really notice a difference. You model in a completely different way basically using sketches instead of CV-hulls and it may take some time to adjust to this. Although when you have and you understand what you are doing, you realize that Catia is a quite logical and stable system.  My favorite thing about it is that you can make changes to your original sketches and if you've built in the correct way Catia simply applies your changes.