I actually liked HF quite a bit. I don't like to be bitter about things, so I was glad that BIONICLE at least got a successor, rather than just being dismayed at the fact that G1 was over.
That said, I think HF had tons of potential...not all of which was realized. I liked keeping the same group of core characters, as their varied appearances were much easier to explain as upgrades, rather than some convoluted mutation/transformation. The concept was really interesting, and every year I wanted to see where the story team ran with it. I just never felt like they reached the maximum potential that they could've. I mean, they had MARK HAMILL as Von Nebula, doing his Fire Lord Ozai voice, and only used him for like...10 minutes. The character should have been more visible.
Also, what exactly was Stormer's connection to Fire Lord? They met at some point, I know, but that was sort of left out to dry.
Savage Planet was...meh. Not too memorable.
Breakout was my personal favorite, because of the variety of villains we got, and I thought that episode was the least cringeworthy.
Brain Attack was alright. The sets were pretty good, but the story was average.
IFB was an interesting concept with good sets, but it didn't exactly follow from Brain Attack. I might get some hate, but it's episode was the best, IMO, because it channeled the spirit of HF the most, aside from Rise of the Rookies. Sure, the identical-sounding voices were odd, but the lines didn't sound nearly as bad to me as they did in the earlier episodes. IDK...