I'm not really sure what to put here.
If it comes down to opinion, I'm going to have to say that I flat out don't like Mixels. Same thing goes for stupid stuff like Spongebob and Ben 10.
I also have very mixed feelings about the "girl" lines. On the one hand, I like and appreciate that lego is trying to stop excluding the entire female gender. On the other, I find it fundamentally flawed that they feel like they have to do things like make minidolls to attract that audience. It's almost like continuing to support gender exclusion, but exploiting it for money. Why can't they make those lines at least somewhat accessible to both genders?
Hero Factory was objectively an okay line with a bad story. I had a personal disdain for it due to it sitting in the place of Bionicle, but now I really have no reason to hate it. Same thing for Legends of Chima; I had to tolerate a year of it before I was able to get my fill of Ninjago again, but now I take no real issue with it.
Lastly, I'm going to have to agree with Spiriah on Monster Fighters. It was played out way too cheesily for my tastes. I loved some of the parts that we got(couldn't get enough of those ghost figs; I must've bought three of those polybags), but overall it was kind of a weak theme.