I haven't played either. Are they really that good?

Legit great game hampered by a poor protagonist design and overall art style. Should've gone with something more akin to Ape Escape and I think it would've done a lot better.

But I had a great time with it nonetheless. But it's also a very long game

I enjoyed both Knacks. That generation was lean to none when it came to games of that genre, and I felt they filled the void well. I do not understand the meme status they received(s), other than the fact that it seems like the internet needs something to beat up on at all times. And once it finds its target... man. It's over.

In my opinion, no. You can safely skip the series. Knack II is certainly the better game, but it's far from perfect. The combat is simple, but fun enough; and the puzzles aren't half bad. The biggest problem, apart from the weak story and dull characters, is how it wastes your time. Knack II is a six-hour game masquerading as a 12-hour game.

If you must experience the series, I would suggest skipping to Knack II and playing with a friend/partner in local co-op.

I'm calling it now: they are jumping straight into Knack 4 to shock everyone.

This thread reminds of how many IPs Sony debuted on PS1-PS4. On PS4 alone, 21 IPs debuted. Granted a lot of them haven't gotten sequels yet, but more than a few have.
PS5 has only had Returnal, Destruction All-Stars, Concord, and Saros. Two of those are live-service games, one of which shut down right away and the other which is shutting down and will have limited functionality after November.
And only a few more new IPs will likely debut on PS5. Intergalactic is all that we know of, I think. Calling Wolverine a new IP is kind of half-true. It's technically set in the same universe as Marvel's Spider-Man but plays way differently of course.

Nah, I played like 15 minutes the first one, it was really bad and the graphics can't even be good.

It became a meme joke on the PlayStation community.