I actually had the same experience as you until I got to the Sand Dragon level. I'm not sure what the difference was, but for some reason, that level was really fun and they seemed to get more fun after that.
If for no other reason than curiosity, give that one a go and let me know what you thought of it. Like I said--I'm not quite sure why that one was so much more fun, but it just was. ??
If you've already played that level, then you're free, but I suggest giving that a shot, and since you have had some very constructive feedback, let me know what you though the difference that adventure had compared to the previous ones.