When the former aired, the only reasonable complaint I saw people give was how harsh the 5 friends were in trying to teach the lesson. Although when you see opinions dissenting from your own, it always seems as though everyone's against you on the matter.
If it makes you feel better, I liked Mare do well and didn't really care for Rainbow Dash's Eco-Terrorism Adventures.

Did a lot of people hate the Mare do Well episode? Eh. I liked it myself. I think it did a nice enough job exploring Rainbow's egotistical side and need for attention. But yeah, how they try to put her as the bad guy, for really doing nothing wrong except bragging (Which no one but the Mane 5 had a problem with) is done pretty poorly. And… how apparently Ponyville suffers from more accidents than any other place ever to exist…

Tanks is just a sympathy episode. People can relate to not wanting to lose your pet, and it has Rainbow all sad and what not. But I will say I don't like how the ending does nothing to put her in the wrong for all she did. (She destroyed a weather factory, causing Celestia knows how much in damage and effecting weather for so many other places.)

If they at least ended it with her having to help fix the damages, I'd have been fine with it. But it's like the Daring Do book episode. Where she breaks into the hospital to steal and all she has to do is apologize for being an "egghead"…