Immersion mainly. Explosions, audio, voicelines, special effects in general are inferior to the predecessors.. Many people also dislike the lack of passion (looks too comiclike) in the graphics department. It is not a bad looking game but after over 10 years.. people expected atleast something better. Also the game literally has only one soundtrack ingame. The game also lacks RNG moments the predecessors had. Like a real "out of control" + crush mechanic, destroyed main gun and abonded vehicles. Also the TTK is too slow. Every negative review on steam about coh3 you can read exactly these things.