I've moved your post to the Premiere Pro forum where you'll have better luck at getting your question answered. You might also try the product page at http://www.adobe.com/products/premiere.html
The more specific you can be with your question, the better.
Welcome to the forum.
Can you tell us about your system, and someone can tell you if PrPro CS 5.5. will be compatible with it?
As for features, each new version of the program usually adds some features. However, a few of the older ones, might not make it into the current version. An example of this was that with the release of CS 5, with MPE and CUDA support, some Effects were no longer compatible, and were either dropeed, or new ones added, as replacements.
Are there some specific features, that you are most conderned about?
Also, there are differences in the Effects and Transitions, between the PC and Mac versions. Knowing your OS will help others to help you.