Good and bad, mostly good.
Good = a clean, quiet ship; every meal began on time; meal servers efficient, attentive -- ready with coffee refresher, ready with a second glass of wine or beer; meal portions sensible; food tasty, nicely presented; breakfast buffet variety of items (cereals, eggs, omelets, sausage, fruit, croissants, jams/jellies, OJ, grapefruit juice, coffee, tea, butter, honey, etc.); 24/7 quality coffee from a dispenser near the lounge; treats (cookies, pastry) always available by the dispenser; sanitary standards obviously a priority, from your room to the hallway to the lounge to the restaurant
Bad = tours to Salzburg and Durnstein too much emphasis on shopping -- not worth the 2-hour trip to Salzburg, although scenery was beautiful; Salzburg bus dropped you off just outside the main shopping district (don't believe the Web and brochure of the Salzburg gardens because it is only about two blocks long and a block wide) and although some free time was available to get to the hilltop castle there was not enough time to actually stroll into the city proper to see neighborhoods and other city life; Durnstein was one long, narrow street packed with touristy shops, with the ancient castle perched above, reachable by a hike on a steep trail, which actually was good exercise; my advice is to skip Salzburg and stay in Linz to see the city there and you'll have all day to do it; conversely, not nearly enough time in Vienna, only a morning tour with afternoon free time -- it's a city worth part of another day, which could be accomplished by leaving Durnstein off the itinerary and just docking in Melk, with its beautiful abbey.
Our ship was first to arrive at three cities and at some point during the evening another Viking ship docked alongside, wiping out our river view. This was especially irritating in Budapest with its grandeur and magnificent views.