I felt a little lost when I first opened GIMP 2.6.11. For a Photoshop user, it's a little like visiting a foreign country for the first time: Some things seem familiar and others are not. Fortunately, GIMP's tool box includes tips when you hover over a tool; and the options for the tool appear in the lower half of the tool box when you make your selection. Also, the available on GIMP's website can help.
For basic image manipulation, GIMP makes it easy to adjust brightness, colors, contrast, crop, etc. GIMP includes a wide selection of built-in filters and effects, like blur, distort, colorize, and transform. Unlike or (both $90 high-end image editors) there are no shortcuts like red eye remover or Cut Out Studio (PhotoPlus X5), which is a shame because I think GIMP would do them well.
Once you get the hang of the layers system in GIMP, creating original artwork begins and ends with your skill level. GIMP's painting and fine art filters produce moderately nice results, but it you're really interested in creating fine art from photographs, try partnering GIMP with FotoSketcher (free), a basic image editor that excels at this.
GIMP is purely a raster program, but there are also a vast selection of drawing and painting tools included. Unlike , another free and open-source image editing and painting program, you don't have to search the internet for the plugins you need: Most will have already been incorporated into GIMP.
There are little things to dislike about GIMP: When you minimize the program, for example, the floating tool boxes remain floating in the middle of your monitor. You can open as many images as you want, but there's no way to easily locate or keep track of them.
Subtle things about GIMP show it's not being created by someone following trends, but rather by a group of people who are passionate about making GIMP better than the trends. GIMP's image open dialog box is a perfect example of this: the navigation is smooth, and it's really easy to see where you are and where you need to be. For a Windows user who's frustrated by the Microsoft trend to make everything as pretty, overloaded, and confusing (Windows Vista or 7 file navigation, for example), GIMP is a blast of fresh air.
If you've never used Photoshop, GIMP is a worthy program for image editing and manipulation. If you're a Photoshop expert, and have either become disillusioned with Adobe and/or its habit of making you $700 or so poorer on a regular basis, GIMP is still a viable alternative, but it comes at its own price: Forget everything you've ever known about image editing and learn from scratch. But with the money you'll save, you can buy a lot of coffee for those long nights ahead.