The falls are twice as tall as Niagara Falls and several times longer and has the longest sheet of water of all falls in the world (although they aren't the highest, widest or largest in volume of water).
The Victoria Falls on the Zimbabwe side was easily viewed by a nice even path, that allowed you to see as much or as little as you wanted or had time for. We spent 2 hours and got to see all of it, but were a bit rushed in parts. We were also lucky it was quieter, without large packs of people to deal with.
The spray in parts was strong, although refreshing on the 40C+ day.
We visited in the dry season, when a large part of the falls were, well dry.
We have also see Iguazu Falls (both the Brazilian and Argentinian sides) and I have seen Niagara in the middle of winter. They are all so different, it's hard to compare.