I'm glad you enjoyed it! The barrel cannons are from the SMWC sprite section, and I don't know how to fix them to feel less "quirky", though, it could just be how the barrels are on SMW's engine instead of DKC's. I didn't use too many barrels for that reason.
One of them seemed kinda blind because of a Zinger, so I added a small trail of coins that'll allow a safer drop to the rope below. The spikes were easy for me to see, despite the palette, so it could be a difference in screen brightness. Though, they use the same palette as the lighter vines.
As for the oil drums, I couldn't fix the ExAnimation due to the amount of tiles they used. The only displaying of the top is because of the framerate differences when the hurt animation happens. The group of 3 oil drums isn't too hard to do, but I'll remove the two upside down drill roses (piranha plants) to make it easier. Then the player will only have to time it with the fire.
Finally, for the Zingers. Terry von Feleday made the GFX for the barrels and enemies. I PM'd him to ask about redrawing the Zingers, but I haven't heard back from him, so I put the normal Zinger graphics in for now.