Gimp can do what Photoshop can do but it will take you twice the amount of time. If time is not an issue it's not a problem.
Some things slowing you down in Gimp:
Working with text. A layer has a size. Out of focus problems of your tools and working area.
Try it: http://gimpusers.com/tutorials/compiling-gimp-for-ubuntu
Gimp can do what Photoshop can do but it will take you twice the amount of time. If time is not an issue it's not a problem.
Some things slowing you down in Gimp: