The most thrilling ferry ride that we have ever taken is the one from Juneau to Sitka through Peril Strait. For me, watching that 408-ft ferry fishtail around the bends in the very narrow strait (cruise ships are too big to travel there) and passing smaller boats like they are standing still was more exciting than watching the Daytona 500!
And I agree that the AMHS ferry crews are incredibly well-trained, helpful, and just plain nice folks. As AlaskaShooter says, these ferries are old and break down occasionally. In 2000, we had had reservations on the Columbia for six months but it had an electrical fire a week before our reservation. It had to be towed into Juneau and was obviously out of service during our trip. The ferry office gave us an immediate refund for that portion of our trip and even made reservations for us on Alaska Airlines (at our expense), so we could get back to Juneau and continue the rest of our trip. Fortunately, the refund and the airfare evened out, so we didn't lose money on the trade.
But we still love the Alaska ferries and will take them every chance we get.