well if we use the esrb as our guide
duke 3d, duke1, and dnmp are rated M
duke2 is rated teen
duke is basically late night tv now compared to modern games.
get blake stone if you want less gore in your fps.
I wouldn't even consider it that gory to be honest. I think Doom is more gory then Duke though some of the cutscenes make me giggle like when he kicks the eyeball through the goalpost.