In creature stage I always liked the interactions between you and your fellow nest mates, like when one of them takings a liking to you. I find it humorously cute how they run up[ to you and shake their tails and waves and everything trying to get your attention. Its cute.
I also like running around in a pack and the little things like when you eat, others in your pack will eat too. Or if your a friendly creature how you can dance and sing in pairs and it becomes the creature version of the greasers and Preps dance off.
I also like the timeline you can view, it really feels like your going through evolution in the game. Overall I really love it, its a blast to play and despite a few glaring bugs I had to deal with off the get go (thanks vista) it runs beautifully on my machine