I've been thinking about this, and I think part of the problem with collectathon platformers is that there's no real sense of player progression outside of the collectibles themselves. When I say progression, I mean specifically skill progression and mastery of the basic mechanics of the game and that's because there's nothing to really get better at in these games. You start them just running around, collecting shit and doing random tasks that are brought up and then forgotten about never to be seen about and you end them... just running around, collecting shit and doing more random tasks that are brought up once and then abandoned. That being the case, when you get to the end of the game, you're kind of just left with a lack of satisfaction because despite having made a lot of progress and accomplished what the game asked of you, you haven't actually really gotten better at anything or have any greater mastery of any of the controls or mechanics, because the game never really requires that, you know?
Like, in racing games, you get better at maintaining your speed and avoiding wiping out and shit. In FPS/third-person shooters, you get better at killing shit without getting killed yourself or even taking damage. In stealth games, you get better at avoiding being spotted even in increasingly more difficult situations. In non-colletathon 3D platformers, you get better at jumping from platform-to-platform in 3D environments without falling off or running into obstacles.
But in collectathon 3D platformers, what are you really getting better at exactly? What's that different at the end of the game, from the start? Because the focus isn't even on platforming and there barely is any (like, Banjo Kazooie has no real platforming of any particular note until Click Clock Woods, the last world in the game, while it introduces flight, a mechanic to entirely avoid it in Treasure Trove Cove, the second world), there just isn't much of a feeling that you've truly actually accomplished anything at the end since what core gameplay there is is pretty static (ignoring the constantly changing minigames which aren't meaningful because they're just there and gone, not giving players time to get attached or care about any particular one or have reason to get better at them) and the difficulty curve basically non-existent, which leaves the whole experience unsatisfying because "skill" is basically a non-factor. Either you get the basic gist or you don't. And that being the case and people naturally wanting a feeling of actually getting better at something, regardless of what that something is (whether it be third person shooter mechanics in the Ratchet and Clank games, focus on actual 3D platforming in the 3D Marios, or whatever), which the genre couldn't give them, is part of why it just died out. Maybe that's just me? But thinking about it, it's what comes to mind.
Like, the only thing to really get better at, is just doing the levels faster and faster and basically taking up speedrunning. But since these games themselves didn't particularly encourage that or give any incentive to play through the games multiple times, that wasn't enough and either they found different hooks or just kinda vanished. I dunno if I'm actually on to something or not with that, but thinking about it, it's what kinda makes sense to me.
We can debate whether or not such gating is good, but it's undeniably a dated practice and that's what reviewers seem to latch on to. What you gain from strict gating seems to be negligible, what you lose from it is pretty tangible. I always felt kinda cheated when I'd spent a few hours in every level and was ready to move on, only to be told I needed to go revisit them and find more stuff.
People get 100% of the objectives in levels they love, and 30% of the objectives in levels they dislike (or aren't good at). So when the player hits the hard progress gate, they're essentially being told to go back and do the things they weren't having very much fun or success with. My reaction to this was usually to just stop playing the game altogether. Did I care that much about a single boss battle or final level? Probably not, but to deny me the ending because I only got 65% of collectibles certainly leaves a bad taste in my mouth.
Some gating is fine, but when a player is ready to progress they shouldn't be locked out by collectibles. Of course this is impossible for a game designer to do, because everyone's sense of progression and fair gating is incredibly different. I suspect that's why this form of progression was eventually dropped.....you can't please everybody, so just give up.
Oh god, this was so me in Super Mario Galaxy 2. Like, okay, Starship Mario uses Power Stars as fuel, right? I got the in-game "justification" for why you needed X number of the things. But there were times I could see on the in-game map that I had enough Power Starts to give Starship Mario the "fuel" it needed to get to the next Bowser level. But yet even though I had enough "fuel" I still had to play through at least one mission on each of the planets that were somehow "in my way" anyway. Like, I don't know how it even makes sense for those stupid galaxies to even be in the way to begin with, but somehow, despite having the fuel I needed, they were just "in the way" anyway. I hated that shit.
And yeah, it's exactly like you said. It's not that I particularly cared that much about a particular level. But sometimes I just didn't feel like doing some stupid slide-level and just wanted to move on to other shit just for a change of pace, but couldn't because stuff was arbitrarily decided to just be "in my way" and stopped me from moving on until I did the stuff I wasn't interested in at all at the moment, which made much more likely to just put it down and stop playing for a while instead of keep playing. Just hated that shit. Fuck the 2D map in Galaxy 2. Shit was garbage.
And yeah, it's nothing like Assassin's Creed or whatever. Because in Assassin's Creed, at least they give you a story reason for whoever your supposed to take out or whatever your current objective is. In say SMG2, on the other hand, there's never any story justification for getting any individual Power Star in particular. Yeah, they say you have to get a specific number of Power Stars, but they never even begin to try to explain why certain Power Stars are more important than others and you have to get particular ones whether you want to or not, and why some are just magically "in your way" and some aren't. All of them seem equally important to each other and none of the individual worlds (aside from the boss levels, of course) have any real story connected or anything, but just due to the 2D map and shit, some of them you just have to do regardless of how many Power Stars you collected because they're just in your way regardless.
Like, when the game at least attempts to provide a story explanation for your current objective and why you're doing what you're doing, it's one thing. But when the game says you have to collect only a certain percent of this garbage, but some of the garbage is apparently more important than other garbage and you have to collect that garbage in particular but the game never explains why that garbage in particular is so special but you have to specifically collect it anyway or else you're just blocked out of progressing anyway? Yeah, that's just really, really frustrating when there's no reason for it being so special and you just wanting to move on because it's not interesting and the game doesn't give you any reason to think otherwise and you're still just content gated regardless. Bleck.