The big criticism of string theory is that its not experimentally testable. But, a lot of recent theoretical research has shown that might not be true. It may be possible to at least test some aspects of the theory in the near future, as this article shows.
"When the world's most powerful particle accelerator starts up later this year, exotic new particles may offer a glimpse of the existence and shapes of extra dimensions"
To get a grip on all these extra dimensions, you may want to order a copy of the upcoming String Theory Demystified: