I like everything listed so far. But I also like shifts in time of day. I like watching the shadows change position.
Idle animations. Seriously, having even just one for the character you're playing as adds so much to any game. A favourite of mine that immediately comes to mind is Mario sleeping in Super Mario 64.
my absolute favorite is in rayman 2,where he starts playing w/ his body
Visible changes to characters is something I love too. Stuff like on the newest Tomb Raider, how you start off fresh and clean and by the end of the game Lara's clothes are torn, muddy, her hair's messier. I do like them touches.
A few things I like from a range of different games/genres:
- Attention to detail
- Subtle references to previous games
- References to pop culture
- Weather effects
- Character facial reactions
- How characters/npcs interact with each other within the world - external to what you're doing
- How much you effort/detail that goes into areas you can't even access
That's all I can think of at the moment. All of what I said don't necessarily make a game, but it's just those little add ons which can ultimately add up. Sometimes it is the bigger picture, but I really appreciate the subtle details; it shows that they game creators really care.