You can also set up custom genres to accomplish what you want
The default genre tags are almost completely worthless to me. So many of the artists I like deliberately cross genres or create fusions of several genres.
For that reason, I've devised a custom multi-attribute genre tagging system, sort of like a dewey decimal system for iTunes.
First, every track gets a decade designation (00s, 90s, 80s, etc.), then one or more genre attributes (blues, r&b/soul, jazz, country, bluegrass, gospel). Artists that cross genres simply get more than one attribute tag assigned to their tracks (this also allows nice track level granularity).
The decade is when that track was first heard, not released - they can be vastly different. I add the remaining tags in alphabetical order.
For example:
Diana Krall = 90s.Jazz.Vocal
Grateful Dead = 70s.Americana.Psychedelic
The point is, one of my custom tags is "PG-13," which I use to exclude tracks with questionable language or cover art from certain playlists (for example, certain Frank Zappa tracks just won't do in certain social situations). You could do the same with a custom "Gapless" tag.
The advantage of genres vs. the comment field is that you can readily see the genres in the default view and re-use them (with auto complete); Comments will always be just free text.