I've taken BC Ferries countless times to the Island and back. I'm not sure how smart it was to increase passenger capacity while decreasing vehicle capacity on the new ones (Super C?). How many walk-ons can really be expected on, for instance, the Tsawwassen-Duke Point route? But the car decks are regularly packed.
As for Marine Atlantic. Once you're on the boat, it's a fine experience (necessary given the length of the routes. In BC I just stay in the car); live music, multiple restaurants and bars, wifi, etc. But they take forever to load/unload the things in comparison with BC Ferries.
@SignalHillHiker: I'm pretty sure some Irish Ferries are much larger (and it looks like there are a pair of Oslo-Kiel ships that are even larger). I was on the Ulysses
from Dublin-Wales and it was massive!