My wife and I did this excursion last June and most of it was great.
Yes, sit on the left if you can, but if you can't the train is so open and narrow you won't miss much. The bus ride down was OK but it took a long time at the border to have the patrol look at your passport and then find your bus and sit there until they let you leave.
I would say the bus trip was 6 on a scale of 10.
I don't know if there are different excursions that exclude some stuff, but the suspension bridge was a waste. It is just a "Bridge to Nowhere" built just for tourist. You can by a drink and snack there and take a picture of yourself on the bridge and you stay too long at this stop.
We also had a stop at the gardens at the edge of town. This is a nice garden that included as part of our tour a lunch. The lunch was nice but the bus driver drops you off and leaves you there for 2 1/2 hrs. That is too long because by the time you finish this tour you have no time to enjoy the town. We ended up just running thru town hitting the highlights and getting a beer at the saloon. If your ship has to dock at the far dock it takes longer to get back to you ship so even less time in town.
On the plus side we are planning a second trip in 2010 to go back and spend more time in the towns and eat and shop etc.
We loved Alaska and will make it a regular trip maybe every other year.
Now before anybody thinks that what I wrote sounds like sour grapes on the train tour, it is not. We liked the tour because of the train ride but wished we could have just gone back to town to enjoy the town.