There are some other stinkers in the mix: Air Ride, Dreamland 3, and Avalanche - but these spinoffs or non-major releases.

Kirby's Return to Dreamland got handicapped by critics coming out so soon after Epic Yarn. If Epic Yarn hadn't come out, it likely would have been in the ~88/89% range in its place when considering other lapsed franchise returns to home-console of similar quality. All the same, Kirby's Return to Dreamland and Epic Yarn both had the majority of reviews being 8s, 9s, and 10s, while Star Allies is mainly 6s and 7s.

This is the biggest decline of any mainline Nintendo series I can think of since Lylat Wars > Star Fox Assault.

Kirby's Dreamland 3 is going to come up, it's a mainline game in the franchise, despite the fact that very few people even knew of its existence. I think I was one of the few people that managed to get my hands on this rare "gem." Most people didn't play this until 2009, and despite the fact it originally launched after the SNES lifecycle, it looked primitive, like a launch title. This was especially confusing considering Kirby Super Star had both up to date visuals and inspired design; this isn't a case of people not enjoying what happened to  DKC3 - as the game maintained trends and advanced over its predecessors; this is more like a case of DKC3 instead going back to the graphics and design of the Battletoads Battlemaniacs design and graphics. It is almost as if they had the game shelved since around launch, opted instead to do Kirby Superstar after, and then later considered "You know what guys? Why the hell not? We're almost done! Let's pull that old Kirby DL3 off the scrap heap!" Considering the obscurity of the title, along with its questionable development (seems like leftovers), I tend to omit it in a similar way that I omit all Harvest Moon games from the franchise after Marvelous stopped making them!

EDIT: And yes, I know Adventure is missing as well, but it doesn't look like Gamerankings recorded any reviews for it.

Planet Robobot spoiled people.

It really did. Hopefully we'll see more of that brilliance in the next one. 

73 is not bombing. 70+ is a GOOD game. 80+ is a GREAT game, and 90+ is a MUST PLAY game.

People have such a twisted and sad view on what these scores mean. Kirby did fine with critics, some fans just do not understand the concept of a 10 point score system (which is why it needs to be done away with because there are even critics that do not get it or abuse it).

Then critics have poor taste.

Probably the same critics who gave Mario Odyssey and Breath Of The Wild 10s, so I don't know...

this not a game i really care for reviews my kids played the demo and have been asking me to buy it ever since. Its just i think this couldve been 40

You say the game got mostly 6's and 7's.  Simply not true.  The game has 5 reviews in the 60-70 range.  10 reviews in the 80-90 range.  That's not counting the ones above 90.  More 8s than 6's.  Probably why the average is closer to 8 than 6. 

Just a quick way to show the strange bias in this post.  It's a Kirby game that's a bit less good than the others in the series, and the score is also a bit less good.  Nothing more than that.

Yeah I think you need to look up the actual definition of a poor score because this isn’t it.

73 is not bombing.