These things are not Viking issues - they are general characteristics of river cruises - yes of course there will be other people at your table, or at least very closely adjacent and private dinners are not going to happen, everyone has dinner in one sitting in one place (unless you use room service) and meals have limited and defined hours, the dining room isnt open all day
On some ships there is a cafe open all day for light snacks - not sure if Viking is one of them but surely you could have found this out before going
and yes entertainment is limited - we enjoyed some fun things like quizzes after dinner - but generally there is no razzamatazz.
If you find that boring, river cruising is perhaps not for you - but it isnt specific to Viking - and again is something you could easily have found out before going.