The concept of Conker's Bad Fur Day is perfect.
A creative and interesting narrative with a lot of humour, providing an amazing variety of gameplay, with some sessions fitting their own exclusive genre. Truly a unique experience, which is the one thing I look the most for when playing a videogame.

The problem with the game though, is that exaggerates too much in the whole "adult-oriented" idea. Pretty much everything in here has to be about shit, tits or asses.
It also exaggerates in the movie references, but this is something that if the person is not familiar with it, it's just gonna be a cool moment. The reason why it might be a problem it's mostly because it sounds lazy. Which wouldn't be the case if the game was more creative with it's references, but sometimes they're completely replaceable, so in that case would be better to just provide an original moment instead of copying one. Also, did the final boss really had to be another movie reference? Come on, it's the final boss.

But yeah, overall a great game.
Unlike it's predecessors 3D platformers on the system, the camera here is simply perfect. Controls feel great too, even though some people have a problem with them when it comes to the first-person shooter sessions, but I didn't mind it at all.
Again cutting ties with it's predecessors, this is not a collect-a-thon. But there is a lot of pure-platforming sessions here that make sure to remind you that this is indeed a 3D platform.
The story has it's highs and lows, just like the comedy, but it never fails to be interesting and charming due to the uniqueness of the game. I was excited the whole time to find out what comes next. And the most important part, the ending, was tremendously good.
All the gameplay sessions work great too. My favorite in that regard is probably the Spooky chapter.
Boss battles are cool, with one of them being extremely unique.
Soundtrack is pretty good. It would be better if there was a new song in the Uga Buga chapter's section instead of a remake of the overworld theme, but because it's so well done you don't really care.

It's really sad that we never got to see the sequel that Rare planed to do, because I think it would have a decent potential to be even better.

For the most part a pretty solid collect-a-thon with some great level design.
But there was something in the final strecht of the game that I'm not sure how I feel about it. I'll get into that later.

All the levels are unique and essential, except the eight one (Rusty Bucket Bay). Don't get me wrong, it's still pretty good, I just think the game wouldn't lose any value without it. The best one is obviously Click Clock Wood, since is the most unique of them all due to it's amazing concept.

Also, what's up with those transformations? They're mostly for cool aesthetic than anything else, since they all have more or less the same kind of abilities (being small and able to walk through any kind of terrain), so I think there's some waste of potential there.

Soundtrack-wise I found it mediocre at best, and that comes from somebody who absolutely loves Grant Kirkhope's work in Donkey Kong 64. Yes, the main tracks are pretty good, and by that I mean the first ones you're exposed to: 1) the one in the opening; 2) the one in the tutorial level; and 3) the one in the hub-world. As far as the actual main levels... Click Clock Wood is good, Clanker's Cavern is nice, and... that's it, the rest I don't care at all.

The game doesn't have any boss battles except the main villain itself, and I personally don't see a problem with it. Also, the one boss battle is a pretty good one.

The quiz is a phenomenal idea. I undestand that some people might have a criticism with the questions about Gruntilda's personal life, but I actually enjoy it, I just don't know if my reason for enjoying was intentional by the developers. I thought it was cool to deal with one scenario that would depend totally on your guess (assuming that at this point you either don't remember the answers or never got to know them). Also, pretty much all of them I guessed right just going by the one that sound more likely, so I guess is don't necessarily have to rely on pure lucky after all.

Now about the ending..

(you might consider this a SPOILER)

After the fake staff roll, you discover that the games is not over yet and you must defeat Gruntilda once for all, but to be able to do that you must collect... everything. Seriously?
First of all, the point of having a lot of stuff to collect in a game is directly related to the fact that they're not all essential, that's why people go after them if they want to 100% complete the game, because you don't need them to actually beat the game.
But yes, every style of game has their own way of succeed, so let's talk about how Banjo-Kazooie's way does, which is kind of the same way as Super Mario 64.
In Super Mario 64 there are 120 stars available, but you only need 70 to beat the game, and that's where the magic comes, because you have the freedom to choose the 70 stars that you want. You get to play on your own rhythm, including dedicating more time to the levels you appreciate the most.
That's the whole point of a collect-a-thon for me: you have a lot of stuff to collect, but you don't need all of them to beat the game, so it's up to you which ones you're gonna collect, and if you WANT to master the game, then good luck collecting all of them.
And Banjo-Kazooie just fucked up the whole point of a collect-a-thon.
But OK, maybe that's not entirely negative. It increases the whole focus of the game in exploration, to the point of being much more close to a metroidvania than a platform (which is cool, I think 3D platformers work pretty good that way).

EDIT (1 year and 2 months later):
Man, looking back now I don't really dislike this. After all, it's not Super Mario 64, it's a different game, and the one thing I value the most when playing a game is to experience something new. I think there is a value in making you collect every single thing, as I mentioned before it expands the exploration factor in the game because now is not just a optional post-game thing anymore. Only when I replay the game that I'm gonna know how I truly feel about it, but at this moment I don't see it as a problem at all, even though I hated back then.