I've heard great things about it from a friend, and am planning a trip in April. While still well off the beaten path, the islands have become much more accessible in the last few years and are already transforming pretty fast. Permits are now available on-arrival at the airport and those islands open to tourism have no hassles, although infrastructure is still pretty bare-bones. A few of the really remote islands, eg. the Sentinels, are home to Stone Age tribes and off limits to
everybody -- some researches were shot at by arrows when they tried to visit!
The best resource on the net, and even that's not saying very much, is probably Wikitravel:
http://wikitravel.org/en/Andaman_and_Nicobar
http://wikitravel.org/en/Havelock_Island