For me, the opposite happened to "jumping the shark", although I'm aware that I'm stretching the definition a bit.
Knightmare started out as a dark, dingy, claustophobic experience which I absolutely loved precisely because it was frightening. I still love the earlier seasons for thatnow. By season 8 it had been watered down. I don't want to sound ungrateful because any Knightmare is good Knightmare, but for me personally, season 8 felt a bit...
"That big scary skull Life Force sprite was too much for little children. So was the walking skeleton-knight. Let's show you a nice pie to track your Life Force, because when it runs out, you're hungry. You see?"
Being able to put clue objects in the bag just muddied the waters for me. Does anyone remember that part in series 5 or 6 when Hordriss, disguised as Harris the Beggar, put a book in the dungeoneer's knapsack and had to reassure them that it wouldn't be digested? That's a nice little mechanic that the Knightmare team created out of almost nothing. How many times have* you* felt anxious about someone putting certain objects in a bag? I admit that my first reaction was "Let's let the little darlings put things in the bag so they don't have to hold them" but in truth it was probably more to do with letting the dungeoneer keep their hands free to use Reach
Snapper-jack as a character came off as patronising, much like the Life Force pie. Thing is, his voice and tone and general weirdness could have made him a fantastic character! So I think it's such a shame they did the hand-puppet thing, and that if they just removed that then they'd have had some extremely unsettling for dungeoneers to deal with
Special mention for that one scene where Brother Strange uses magic to open the trap-door to level 2. I forget his exact words but it's something along the lines of "this is a very dangerous moment. You must keep very still" before he stalks around the door, knocks it with his staff, and it opens. It just fell so flat to me. How could this possibly feel dangerous? Compare that with "Harris" putting the book in the knapsack where it was fairly clear what the potential danger was. Perhaps if they'd introduced a mechanic where something dangerous might be lurking on the opposite side of that trap-door that the dungeoneer had to get rid of without encountering it direclty then it could have worked brilliantly.
It felt like there was just too much CGI. Yet, even this I think is forgiveable because one of Lord Fear's main strengths was his willingness to innovate. This too could have been utilised better. We as viewers were expected to ignore the obvious CGI, but what if there'd been some cover-story that Lord Fear had extended his influence even into Level 1 so that it looked like his territory but his magic there was weak? That could be explored so much, but what could Lord Fear have done under those circumstances? Generally unnerved the dungeoneer? Created the illusion of monsters where really there were none? Nettled clue room guardians into asking harder questions?
Like I say, I don't want to come across as ungrateful for any Knightmare show. I just think the above could have been better used.