Megadeth: Rust in Peace
The best goddamned thrash album of all time, and possibly the overall best Metal album of all time. The epitome of short (barely 30 minutes in length) but sweet, this album has no filler; no unnecessary moments. If this album were any tighter, it'd crack the CD it comes in. Each song has so many amazing, off-the wall, intricate but still heavy as shit, bang your coconuts riffs that you could pick 3 at random and make a whole album out of them. Even the weakest track (Lucretia) is better than 99% of all thrash. The arrangemtents are ambitious but uncompromising and show that metal can be intelligent, complex, calculating and precise without losing its teeth and its razorsharp aggressiveness and most importantly, without falling into the pretentious and bloated trappings of prog-rock.
Marty Friedman's laberynthine solos and vibrato are an exquisite yang to Mustaine's angry, shreddy yin, and Nick Menza's clockwork drumming infuses the song with a jazzy sensibility that somehow fits thrash perfectly.
It's a pity that the band would slip into a downward spiral after this. Countdown to Extinction is as best mediocre, domesticated and predictable metal that reeks of mainstream compromise. Youthanasia is such a soulless, bland, colorless, written-for-radio piece of sellout trash that it's almost incredible that it was written by the same people who made RIP.
I also consider
Miles Davis's Kind of Blue to be equally perfect. I wrote a couple of paragraphs about it but I lost them (stupid Evernote -.-) and I don't feel like typing them again.