i think on some of the challenges you should be able to pick your character but it should be rare imo, nothing wrong with more challenges though and i dunno maybe a decent reward at the end(like they promised)
I think the challenge tower is good because it helps you train with different characters to become more rounded.
But, can you choose your player for the last level? Or is it just Liu Kang? Because on that part I want to choose someone Im better with.
I like it with different characters that way it adds to the CHALLENGE and even though you suck with the character and its CHALLENGING you should be able to overcome the CHALLENGE with practice and determination. I finished all 300 challenges and I didn't find a problem at all with using different characters as you only had to learn about 1-2 combos and then 1-2 special moves and you would be good. Also it would get boring and repetitive as said before. Also now (Probably Story mode helped as well) I can use just about any character and pull off combo and special or two. It also advertise other characters that you might not even know your good at!