Overall I'm disappointed in Legends. Origins was a much better game imo. One of the things that made Orgins so great was it's difficulty which has been has been dump down by A LOT. The invasion mission in Legends are very easy and getting the gold trophy for collecting lums in a level is also very easy, I only remember 2 or 3 levels were I had to restart because I didn't had the 600 lums for the gold trophy.
The music stages (specially the 8 bit ones) were probably the best part of the game, but overall I'm disappointed. Not saying is a bad game, but Origins was better.
As for the sales, well it's expected, is very close to other big tittles so those will obviously have a priority for more people. We won't know if the game would have sold better as a Wii U exclusive, but like someone said, MH Tri and Lego City sold decently well, so we can assume the same could have happened to Legends, most Wii U owners were desperate for software at the time. Delaying the game kill the hype for a lot people. And advertisement could have also been a big problem.
Nintendo and PC gamer
