It's an incredible album. It's pretty ridiculous that he's doing it all with a guitar and one pedal and some fairly basic laptop stuff. He can't do it all live (one of my favorite songs of his, New Animals from the Air, is impossible for him for example) but he always plays 'Taken' and it's a blissfully loud and impressive 16 minutes when he does.
I think Copia has some beautiful moments. He writes pretty simple yet stirring piano pieces and the hum of horns, organs and strings, all manipulated and altered, are gorgeous on tracks like 'Requiem on Frankfurt Ave.' and 'Ostinato' and others.
I would suggest looking at 'Harmony in Ultraviolet' as a first Hecker album, personally. That may just be a bias since it's the first one I heard but it was definitely a good jumping off point for his other albums. Avoid, for example, 'Radio Amor' first as it's less accessible and such. I also didn't have strong feelings either way for 'An Imaginary Country' so don't go for that one first either.
Michael, you will probably like the band Belong as well. It's a duo that makes very dense, pretty guitar drone. Jasper, TX is another solo ambient artists that you'll certainly like if you enjoy Eluvium. His albums are often a bit darker, somehow more sinister I feel. Anything involving Hildur Gudnasdottir or William Basinski will almost certainly be excellent. Finally, for a "classical" ambient sort of piece, Gavin Bryars 'Sinking of the Titanic' is an incredible piece of music.