For me, the major things that make TS4 feel empty are the lack of the ability to create your own world to play in, start a game with all worlds empty (without save manipulation and reserve saves), or add more lots to worlds; the lopsided emotion system; how poorly integrated traits are; and the length of time it's taken, on average, to add new supernatural content to the game.
All of these things make the game feel smaller by limiting replay value, making our sims feel far less emotionally complex than in TS2 and TS3, and severely limiting the storytelling options for supernatural players for insane lengths of time. Seriously, for two years, if I wanted a non-human sim, all I had was aliens and ghosts. Then, vampires came along and for the next two years I had a whopping THREE options for the NEXT two years (two in CAS, one from going through the arduous process of killing a sim , then re-recruiting them into a household!). TS4 has the best CAS and Build Mode, but content and gameplay wise it's...messy...
