Abducted and the self-titled are both masterpieces, and any CD collection becomes better with their presence. A good starting point would be 10 Years of Chaos and Confusion if you are unsure. Here's a breakdown to help you out...
Penetralia - pretty standard early 90s death metal, good for the time.
Osculum Obscenum - standard early 90s death metal with a little bit of the atmosphere later Hypocrisy would bring.
4th Dimension - very good, the first album that defined their sound. Lots of atmosphere, keyboards, but still very firmly rooted in death metal.
Abducted - The greatest metal album since Megadeth's Rust In Peace, this album is KILLER. Lots of shred and mid-tempos, lots of different vocal styles to keep everything fresh and diverse.
The Final Chapter - Take the sounds of Abducted and expand them a bit, my only problem with this album is it doesn't flow as evenly as Abducted and the self-titled albums do. Shred, mid-tempos, slow, moody, etc. However, it has my favorite Hypocrisy song, A Coming Race!
Hypocrisy - Take the atmosphere of the mid-tempo moments from Abducted and make an album out of it. Sheer perfection.
Into the Abyss - Written and recorded in under a week (so I have heard) and sounds like it (no, not a bad thing). Pure raw aggression, sounds like the first two albums with only a slight bit of the atmoshere they came to be known by.
Catch 22 - I don't care what anyone tells you, this is a good album. A little more toned down, especially following Into the Abyss, but still pretty aggressive.
Hope this helps!
Oh yeah, and no I do not have Destroys Wacken just yet (I know, I know, blasphemy), but everyone tells me it is outstanding.
