Half of the songs of most German Rap albums are really boring snoozefests. Shitty beats, lame rhymes, overuse of vocal effects and some features that just deliver stupid cliche lines that don't offer anything of value.
On most Black Metal albums that goes for about a quarter to a third. Lame riffs, recycled leftover lyrics that were thrown out of the better pieces, lame and predictable bass lines and dull, uninspired vocals.
I'm not familiar with most other music genres. Care to extend based on your impressions?