This music sounds like it's about as old as I am, but nobody came into this expecting innovation. Thrash in general is, to a certain extent, predicated on a lack of progress since when thrash progresses (both stylistically and historically) the result is generally either death or black metal with some thrash roots rather than thrash proper. That's fine, though. All a good thrash album really needs to be effective is good guitar work and intense delivery, both of which Overkill deliver in spades.
Cool riffing, effective lead work, snarling high-pitched vocals, overall tight musicianship, relentlessly headbanging groove, and a sense of balls-to-the-wall rocking out energy all mark this album as a perfect example of thrash done right. The drum beat is propulsive, and even the bass gets some interesting sections. There's really nothing much to say about it beyond that, since it covers very familiar territory and it has no discernible flaws. Basically, it's just a really enjoyable album that anyone with an interest in '80s thrash should thoroughly enjoy.