Unitron
With how experimental the 90's were for music, to define the sound of a genre in the decade may seem hard. However, somehow one of the first albums I think of when I think of metal in the 90's is Helmet's classic Meantime. Blending post-hardcore, grunge, and groove metal, it acts as both a mix of some of the best stuff the early 90's had to offer and a fantastic prototype for future alt metal and nu metal to come later in the decade.
There's something about Page Hamilton's monotone version of melody mixed with punishing hardcore riffing that just works so well. Though when he's screaming, you basically have sludge without the doom in crushing songs like Ironhead and Turned Out.
The album is just 36 minutes of hard pounding metal for a workout or release of anger. There's no room for anything less, and each song is a guaranteed angry good time.