Hmmmmm....
First thing that struck me (and I havent seen hardly any vids leading up to the demo), were the graphics. At least FN3 tried to be realistic, this is a cartoon

Pretty poor (though I appreciate the graphics and details etc are 'good', just shocked me as I would have preferred something more realistic) - a step back from FN3 I feel.
Gameplay is pretty much the same as FN3. Think the punching speed is better being faster and the whole thing plays a bit better than FN3, but it just doesnt feel right somehow.
Think I will still get it, but its touch and go at the moment! Only thing keeping me positive is the career mode sounds good (multiple belts, pound fo pound etc) and the online modes.
Feel a bit flat about the whole thing now...
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Oh and what the fuck is up with the headbutt? Very poor... like an arcade game