Don't get me wrong, the Black Album was good and all, but that album and the stuff that follows (except for maybe Death Magnetic) doesn't hold a candle to anything made before it.
Kill 'em All - Straight-up thrash metal. I think Kirk's best solos came off of here, seconded by Ride the Lightning.
Ride the Lightning - My 2 favorite Metallica songs come off this album (Fight Fire With Fire and Fade To Black). Could definitely be a contender for their best album or at very least a very close second.
Master of Puppets - IMO, their best album. Every track is a unique masterpiece. Very fun album to play along with if you're a guitar palyer.
And Justice For All - Great album, but doesn't have nearly as many strong tracks as it's two predecessors. Half the tracks can be pretty forgettable. And for pete's sake, but some damn bass lines in here finally. There is no reason why Metallica can't remaster this album and restore the awesomeness of Jason Newsted's bass for us to enjoy.
Black Album - Good album, but they ditched thrash metal for mellodic power metal and picked up former Motley Crue producer, Bob Rock....this was the begginng of the "dark ages" for them.
Load - Actually the first Metallica album I ever listened to and thought it was decent...and then upon discovering Fight Fire with Fire and Disposable Heroes, promptly chucked this thing to the bottom of the pile realizing how vastly inferior it was. Begginning of their "Alice in Chains" phase. Not bad, but not good either.
Re-Load - Very forgettable album.
Garage Days Re-Revisited - Both CD's were pretty good. Definitely liked the older cover CD better (Am I Evil and Blitzkreig = awesome). Probably the best thing that came out for that decade album wise.
St. Anger - My least favorite album by far. Sound quality/recording/mixing was awful, solos are completely absent, boring and over-simplistic nu-metal riffs, Bob Rock on bass....gah, it sounds like they were trying to copy System of a Down only they didn't come anywhere close. Some of the songs sound good live, but overall bleh. Best thing on this album was Lars' drumming (yes even with the "ping" snare drum).
Death Magnetic - First good thing about this album: Bob Rock is not producing it anymore and has been replaced with Rick Rubin. Second best thing, standard tuning is back (makes it sound more like their early stuff), thrashy metal songs are back, instrumentals are back and most importantly, solos are back! Best thing they've put out in 2 decades, IMO. I almost like more than than Justice, either way it's definitely up there near the top.