We try to include as many new releases as possible, in a variety of genres. Generally, major pop, rock, rap and alternative releases will be included. We also try to include many indie and electronic artists, as well as major releases in other categories (country, etc.). Occasionally, we will also include import-only items (generally, UK releases) if it appears that they will not be released in the United States in the foreseeable future (otherwise, we will typically wait for the U.S. release). Remember, if an album does not show up in at least 3 of the publications we use, it probably will not be included on the site.
The sheer number of music releases each year (over 30,000 unique titles per year in the U.S. alone--and that's not counting reissues, compilations, etc.), compared to movies and video games, makes it virtually impossible to cover every release; thus, our music section is more selective than our games and movie sections.
Regarding our historical coverage, our database currently goes back to the beginning of 2000, with a handful of releases from 1999. Over time, we will add additional older releases, starting with 1999 and working backwards.