Finished this over Xmas and echo a couple of the thoughts on here - the bosses are tough and introduce some tricky attacks to use, which you've not had to use previously. And the collectables must be the most pointless in any game for years - collect hats for your rot. What happens when you buy new hats and put them on your rots? Er, nothing - the rots following you around just look different (although I did actually like kitting them out in Santa hats, to be fair
). Yeah, I know, you could argue that a lot of collectibles, apart from for the benefit of trophy hunting, are a bit pointless but the ones in Kena feel even more so!
Speaking of trophies, I only have a few left and don't feel encouraged to go on. There are three combat ones (like use the same dash to kill three enemies) that you can't get post-game if you have killed all of the random enemies during the game as the amount of enemies throughout is relatively sparse (and they don't respawn). The last two trophies would be completing the game on Master Difficulty (during which I could, if skilled enough, tick off the combat ones) and the Platinum.
Don't get me wrong, I enjoyed the game - 7/10 - but there was something lacking to push it that a little higher for me.