There are many places to go to research ATMOS. I wont repeat the whole story here but here is the readers digest version.

To use ATMOS you need to add height (and optionally wide) channels. This is accomplished by using atmos enabled speakers, atmos modules or in ceiling speakers. In ceilings are the best option.

You also need an ATMOS processor. There are currently many AVRs offered with this feature. They are still very expensive, and having sampled an upper tier model personally, are not worth the current asking price.

ATMOS is the first of the object based immersive sound formats. They will soon be the standard soundtrack on bluray titles. The other current formats are AURO and DTS:X. DTS:X is not slated for launch until March, when more details will be available.

I have experienced ATMOS, along with others here and can say without hesitation that even on non-atmos content it is a worthwhile technology.

Whether or not the added cost of more speakers and amp channels to drive them (new avr/processor) is up to you.