Lightroom is what we like to call a 'work flow' software. It is a pretty good tool to help you organize, catalog, rate and label (keyword) your image collection. It is also a pretty powerful image editing program, but it has it's limitations. It allows you to do most of the global image adjustments like adjusting brightness (exposure), color, sharpness, clarity, sharpening, noise removal etc. It even allows for some targeted adjustments through the use of gradient filters, spot removal and the 'adjustment brush'. It does have an 'auto mask' option, which lets you target some areas while avoiding other areas, but it's far short of what you can do in programs like Photoshop CS (or Photoshop Elements) because those programs allow for multiple layers, layer masks and advanced masking tools.
So if you want to take someone's head from a photo and put it onto another body, or if you want to cut something out and put it onto a different background...that type of thing requires a program like Photoshop CS/Elements (might be able to do that stuff in GIMP).
But that is stuff that I would call image manipulation or pixel editing. If you don't need to do that type of thing on a regular basis, then Lightroom would probably do most of what you need to do, most of the time. As I like to say, Lightroom does 90% of what 90% pf photographers want to do, 90% of the time.
Lightroom also has a great Printing module, as well as modules for creating photo books and web galleries etc. It also has a Map module where you can use or add GPS data to incorporate location information with your photos.
As a 'work flow' software, Lightroom really shines when dealing with a large number of images. It allows easy and efficient editing of many images, without having to go the traditional route of opening and saving each image. But if you don't need to edit large numbers of images, you might be more suited to something like Elements.
But really, the best solution (IMO) is use Lightroom as your main workflow software, and combine that with a pixel editor like Photoshop CS or Photoshop Elements (or maybe Gimp).