My impression, after our Gate 1 trip last fall on the Danube from Regensburg to Budapest, is that Viking and Gate 1 are very similar.
(The only difference, as many have said, is the amount of wine you're allowed for free. But I'm an enthusiastic wine drinker, and I don't think I paid for more than four glasses the whole week we were on the ship. And the prices per glass were less than $10.)
We had one good included tour every day, and sometimes two, and were often offered another at an additional cost. Frankly. I don't think I would have wanted the extra ones (except our trip to Salzburg and the Hungarian folk dinner) because we'd had enough exercise for the day. Often we walked around by ourselves, and sometimes we lounged on the boat. It was perfect.