Unitron
The Years of Decay's album cover is a great representation of the album, sounding like entering the foreboding temple in places, though not without the fun that's synonymous with Overkill. Lumbering grooves meet rapid moshing perfectly with Time to Kill, Elimination, Nothing to Die For, and especially Birth of Tension. The instant headbanging short groove at around the minute mark on that song is one of my favorite moments in thrash. They also perfect grungy doom thrash with the colossal Playing With Spiders/Skullkrusher and Who Tends the Fire, and is a sound that I wish more thrash bands would play.
D.D. Verni is one of my favorite bassists, and his perfect thumping tone has never sounded better, and even throwing in a bit of funk in Nothing to Die For. Bobby Blitz's is one of my favorite vocalists, with few coming close to his charisma. So much attitude and so much fun, even when the music's at a doom crawl he's bursting with personality. The production helps everything as well, having what I'd call the best for a thrash album. Fantastic low end bringing the best in the bass and the guitars and drums have some real oomph.
There's a Metallica album and a couple Anthrax albums that are higher on my personal favorites list, but Overkill's The Years of Decay is my idea of the perfect thrash album. It just includes everything I love thrash for, and done in the best ways to really get me hooked.