Been playing since sat (got pre-order from Tesco direct early) - its okey, think I'm about 35% or so in - canny, but not as good as the first.
Some things feel more streamlined - like having plasmids and weapons available at once, but other things feel dumbed down (like missing uinvent, the tonics being 1 type etc).
The art doesn't seem as nice either - the ocean floor looks wayyyy too colourful imho, whilst interiors feel 'muddy' or just not as sharp as the first.
Probably worth picking up still, but I'd recommend waiting til its slightly cheaper then rrp.