I really like the one where you have to shoot the chickens falling down on you. It's fair for everyone, relatively easy AND a lot of fun!
On the other hand, the one where you have to land on slime blocks is my least favorite - if you land on the edge of a slime block, above lava, so technically not on the ground, you still die. To make sure this doesn't happen, you can use the glass floor to align yourself with the middle of the block, but it's still something that's just frustating...
And about the boss minigames: I don't really like any of them. Many are PvP-heavy, or aren't easy for casual players. The 3-point reward is what I like the least about the boss minigames, as they can easily turn the tables and cause you to lose last-second, which is very frustrating. I understand that they're worth 3 points for this specific reason - giving players a chance to catch up and win - but I think that should have been done differently.
The spleef one is alright, even though it's laggy for players with smooth lighting on because it's floating over the void. Breaking a block that is part of a platform floating over the void causes the client to re-calculate the lighting, which in turn causes lag, making the best boss minigame unplayable for me, despite my computer being more than capable.
All in all, I like the game, but some aspects of it can be pretty irritating.