I am a great fan of Amorphis. Gosh... for more than 10 years now!
Tales From The Thousand Lakes was the album that got my attention. It's basic Death Metal, but with some light, catchy folk tunes. A classic.
Now, Elegy...
If you check the "Perfect Albums" thread, you'll see that I mentioned this one there. It's probably my all-time favourite album and it's definitely the one I heard more times in my entire life. I could play the whole album from the beginning to the very end in my guitar.
Anyway, it was a more complex - although "lighter" - album than Tales..., and it had more clean singing in it. It was more folky as well and all things together worked wonderfully.
Enough with the crap talk, but let me say that everyone who comes to this thread should listen to this one.
With Tuonela, Amorphis went in a new, more mainstream direction. It was hard for me to accept their new sound, but eventually I ended up liking it.
With Am Universum they evolved in their new sound and produced a much more mature album than Tuonela.
These two are similar, but if you have to choose just one of them, definitely go with Am Universum.
To end this in a short way, Far From The Sun was pure crap to my hears and I gave up on the band.
I haven't heard the new album, Eclipse properly but I read that they are again going in a new direction. The vocalist is new in this album as well.
EDIT: Oops. Sorry about the testament.