Well, the symmetrical maps are good because they are balanced and easy to know where you are at and where to go because of similarity, but...
I am a very big fan of the different bases. This adds more variety. I think they are balanced in their own way, you just got to find which one better suits your style of play. Alot of times one base has a slight offensive boost while the other has a little better defense.
If you still think they are unfair, you can always alternate though.
Overall, I think it is a cool addition.
My favorite(only including the ones that came with the game is (this is tough) probably november but eternal caves is real cool too, oh hell, they are all great!!!!