I must admit, I've not watched Fear Her in years. I may have to take a peek this weekend to see if it's as poor as I recall.
To be fair, I remember it being a weak episode as opposed to appalling so I will take another look. I really loved the 10th Doctor and Rose and I think when you have two lead characters that you really love, it probably helps when the episode itself isn't great.
It's one of the reasons I (personally) have a soft spot for Love and Monsters, because it gives Jackie Tyler such a major role throughout the episode and actually there are some key parts of the episode that are just hilarious.
I guess the problem I have with an episode like Heaven Sent is that it's a gloomy and (I felt) rather dull episode starring a Doctor I'm not particularly keen on who was mourning a companion I was glad to see the back of. Would I have liked it more if it had been Doctor 9 or 10, mourning the likes of Rose or Donna?
I would never say Heaven Sent was a poor episode because I think in terms of acting, writing and production values it was clearly of the highest standards.
I simply didn't enjoy it. In many ways it demonstrated everything that (for me) is wrong with Doctor Who at the moment - grey, funless and lacking sympathetic characters. But then I've had problems with the lead characters in Who since Moffat took over.