Music. It's bland and ambient, and is the same for all factions and in all battles. I've been thinking about what makes Rome 2 seem so... lifeless, and I think this is it (more so than the missing cinematics, UI, faction intros, etc.). I think it is often overlooked when focused on visuals, but music and sound are 1/2 of the sensory input you get from any game and make a HUGE difference in the atmosphere and immersion. In Rome 2, its not that the music is bad, it is just... forgettable.
I think this is why so many people feel the game lacks immersion and is 'soulless.' Total War, for me, was never the type of game where you turned down the sound and played your own music. You needed and wanted the music in previous titles to set the tone, add drama to battles, and pull you into the time period. But I think they basically viewed the music as window dressing when designing the game, and didn't put that much effort into the composition. It is just there. It doesn't specifically detract from the game, but doesn't really add to it either.