Went on as panels, about 6"x12" (or perhaps a bit larger) - looks like slate. Appearance is fine! And yes, the snow does slide off - with quite a noise. The installer put up fences on the roof to protect doorways from the slides. Other affects of the slides are on gutters (tends to tear them off) and shrubs (tends to crush them).
The aluminum shingles are expensive - probably 2 to 2.5 times the cost of asphalt. But it's a 1 time job - the last roof you'll buy (until you move, like we did. New owner is thrilled with the roof).