I've just about beaten the game and I really do enjoy what I've played so far. I think I will try and go for 100%, though it does seem like quite a frustrating experience. With that said, there is an overall feeling that I really don't like about the game.
Compared to other platformers, like Super Mario, Rayman, or Sonic games. It feels like Crash 4 is so overly focused on challenging the player at every moment. Even something that would be a simple reward in other games, like smashing some blocks in a Mario game, can provide a source of challenge in Crash 4, with it not being uncommon to find TNTs or Nitro's intermixed into groups of boxes in order to trip the player up.
These elements aren't an issue individually, they're not overly difficult individually, but the feel of the game is one that at least for me, never really feels like it aims to reward the player, or provide any respite for pure enjoyment. In Sonic for instance, you might go down a big hill and in effect, the player has to do nothing but watch the spectacle, in Mario Odysey, you might have a segment with a T-Rex where you get to walk around and destroy everything. In these games, these mechanics are fairly frequent and offer no real source of challenge, they exist for the experiential pleasure alone.
Crash 4 doesn't feature anything like that. Every single element of the game has multiple layered sources of challenge (usually level hazards, and the challenge of collecting all of the boxes), and as a result I find that it feels overly intense. The box collection mechanic in particular means that the player always feels pressured to perform.
These mechanics also cause the levels to offer very little flexibility to how the player approaches, and plays them. There's always an incentive to collect all of the boxes you see in front of you, and even if you're not on a perfect run, it's always worth trying to pick up every single one of these and aim to get the gem for box collection. There's never a state in the game where it feels like you can play the level in the way that you want, or just for the sake of completion.
For instance, there's a segment later on in the game where you get to ride a certain vehicle, and this segment should be a really cool moment that throws back to the earlier games, but during this you're going to feel obligated to collect all of the boxes. So this fast paced gameplay segment can easily turn into something terrible, as you die over and over trying to gather every box.
If you compare this to something like the musical levels at the end of Rayman Legends, where the player is forced forward at break neck pace, it's night and day, because Rayman never asks me to complete those levels collecting absolutely every lum, I can simply do my best and enjoy the experience. Rayman's collection totals are still strict, so it's possible I get to the end and I've missed to many, but I never feel like I might as well just restart or suicide if I miss anything. That objective / reward flexibility allows the player to play the game at their own pace, whereas I feel Crash 4 overwhelms the player with difficulty, and often that detracts from intrinsic fun factor that a level or mechanic should hold.
I think the bonus levels are another good example of this, and one of the most frustrating elements of the game. In the previous games I used to see bonus levels as a respite from the challenge of the main level. They didn't cost lives, and usually they weren't too too difficult, and it usually wasn't confusing how to achieve everything in the level. But in Crash 4, it feels like these segments are designed to trip the player up. Tap the wrong ! box at the wrong time and you're going to screw yourself over. These levels feature both challenging puzzle elements, and intense mechanical demands on the player in the form of platforming accuracy. While some of the later bonus levels in the previous Crash games were like this, most of them were quite easy, and they offered an opportunity to reward the player with a tonne of more lives. That sense of reward is almost entirely gone in Crash 4 (perhaps an inadvertant consequence
I would contend that on the whole, the average player whom will never see the 100% completion badges, would get more enjoyment out of the game if they simply decided to forget the boxes, but that's difficult to do when so many of the rewards are tied to them (since they give Wumpas, meaning they occupy 4/6 of the gem slots on each level).
This difficulty is confounded by two features of the games design. 1) Levels feel quite long, longer than they are in previous Crash games, meaning that the relative punishment for missing a box or dying is significantly greater. 2) The linear level design wherein the player cannot backtrack to collect anything, means that again, the punishment for missing a single box is much greater than something like Mario Odyssey.
I feel as though if Crash wants to evolve it's formula it should think about how it evaluates the players performance and rewards the player. While the level design is generally excellent, the tasks imposed on the player can often suck the fun right out of them. I would have liked more attributes of the exist purely for their experiential value, and objectives that encourage the player to play the game in a more flexible, and fun way.
For instance, if the game never asked players to collect everything, and avoid death at the same time, that would free the player up to take more flexible routes on their 0 death runs, and encourage different playstyles between the two. Another example of a means in which to encourage flexibility would be to forgive the player for missing a certain number of boxes. I'm not saying that's how the game should be designed, but I think that Toys for Bob should think about the level objectives and how they interact with the play experience.