I like that Mathematica has tons of resources on "how to do xyz" out there because it is so widely used. It works well for my research that involves data analysis and fitting Lorentz oscillators and drude terms. It is also based from WolframAlpha, a website I've used many times in undergrad.

The graphical interface and the overall usability is pretty straightforward. The UI is well designed and logically built. The animations are also cool. System Modeler requires no add-ons. It fully supports the Modelica model language. The drag and drop methodology allows the user to create complex systems quite effectively. It can provide many enhancements to my existing libraries. The ability to do noumerus analysis on the model is very useful. Pobably one of the best tools for SysMl and UML modeling.

When doing research, you come up with a model which sometimes is so hard to solve. With Mathematica, you are able to solve any mathematical problem with a single click. It has an efficient and versatile feature that helps in data visualization and presentation.