It's comprised of 90 (!) different tracks, including all the classic themes - you can see the track listing on the iTunes listing page. It's priced at £10.99 in the UK, if you're wondering what time-travel to 2004 will cost you.
More soundtracks from classic games are coming in 2014, The Pokémon Company asserts. After many years Keza MacDonald is still not bored of writing about video games, which is just as well, as her skills at demon-slaying and pretend guitar are pretty much non-transferable. You can follow her on IGN and Twitter.