Reign In Blood is the most overrated thrash album ever. Angel of Death = PWNAGE. Raining Blood = SLIGHTLY LESS PWNAGE. Everything else = mediocre, repetitive, fast just for the sake of fast.
Hell Awaits beats the holy living fuck out of everything else Slayer's ever done, and in terms of sheer fucking heaviness and riffwork there was very little around in 1985 that could touch that motherfucker. South of Heaven & Seasons are awesome too, and Show No Mercy is a nifty little slab of old-school speed metal.
Let's not talk about what happened after Seasons.