My six year old son spent the last of his Christmas money on this set, and to be honest it's a really good piece of lego engineering and a good play set to boot. The main carrier needs lots of building as it has several interesting features, the propeller pods at the front pull back, the sides drop down to uncover a lab, there is an opening bay at the front for a vehicle etc.
You also get a manta ray and underwater mant warrior, an underwater car which fits in the bay at the front of the carrier (it even stays in during play) and a small version of the wreck raider set which fits nicely at the back. There are 3 additional lego atlantis figures, one for each vehicle. Expect bits to move/fall off whilst it's being played with, rebuilding is part of the joy of lego afterall.
There is a lot of building and if you give this to a younger child you can fully expect to be building it for them, my son has built most of the earlier sets and was really proud of the fact that he did it all himself.
A really good lego set that I wish had been available 30 years ago!