I've travelled extensively, and I think I'm reasonably picky about standards. I have read that Viking is not top of the line and I have not been on any other river cruises (so I can't compare), but I was happy with the Viking cruise that I was on.
The staff members were very good, and the cruise director and concierge were exceptional. The ship was spotless. I'm sure that there are lines with more gourmet food, but I thought the food was good, and I didn't hear any concerns from the people we travelled with. Portions were plenty big enough for me: I know that there are endless buffets on ocean ships, but that wasn't important to me.
Regarding the included excursions: the local guides ranged from reasonably good to very good. The evening entertainment was a bit dry or amateurish a couple of times, but the rest was fine. I wasn't expecting any evening entertainment, actually--something else that wasn't important to me.
I've heard some concerns about WiFi. Inside the boat, the only time I had an issue with WiFi was when we were going through locks. It was unavailable on the sun deck, which was disappointing. I survived, though, and I'm very attached to my laptop/iPad.
Regarding the open seating: I was with my spouse and another couple. We hooked up with some other couples throughout the cruise and ate with them. I guess it depends on how much privacy you want, but I found it interesting to talk with other people with different backgrounds.
Regarding the flooding: Trips just before ours were cancelled due to flooding. We were not expecting to get to Passau. We did, but we docked in a different place. No biggie. Think of the locals who had their houses and business flooded. There was also a broken lock. We couldn't sail east, and a sister ship couldn't sail west. We had to pack up our stuff, be bused around the broken lock, and be put on the sister ship (in the same room). Yes, that was inconvenient, and we were disappointed to miss a picturesque stretch of river. But I cannot blame Viking for that. We would not have cancelled the cruise based on that problem (not that I had the option), and we got a 25% credit for a future cruise.
The bottom line is that we were satisfied enough to rebook for 2014, with another couple. (I do wonder whether the "half-price" deals are really permanent sales. I don't like that kind of sales tactic. Does anyone pay "full price" for these cruises?)