This acrylic plastic took work to do… but i need training much more.
What do you want critique on? The pen looks realistic but the scene is plain. I assume to showcase the pen better? Is the image for any kind of purpose? If you want the pen to look more realistic you could add imperfections like scrapes in the plastic. You could also add a brand or some kind of numbers to the side. It would also look more realistic if it was in a scene with other realistic objects or on a table next to paper for example.
Is a plain scene because the focus is only in the plastic. Today i am trying create some glass (lamp) and now i can see in this scene the same problem in cycles glass… The transparent plastic is absorbing light… (is black). I need study more about shaders and glass to create true transparent materials plastic and glass.