I am not finding it that hard to stay alive, i am playing in normal difficulty on hardcore mode. Granted I am only level 7 but have not died, got close when I managed to get rushed by 9 Ghekos.
Apart from where i screwed up at the start and put 15 points extra in unarmed, i am now spreading points on melee and guns. and will save as much of the rest for survivor and science etc. Iron sight is much better than FO3. I tend to land around 2 shots on an enemy at a distance then finish them off with a bat or something.
In hardcore mode it is important to heal up early and remeber that a lot of the heal per second items stack (maybe they all do not sure) So if its hairy u can use some cooked meat, healing powder, sunset drink thing, stimpack, water etc to get yourself healing quicker than you are likely to take damage, buffout seems to be the only thing I have found that gives u HP upfront when u get surprised, these seem rare to get hold of though.
Loving the game, took me 10 hours and 7 levels just to get to primm. Time to fire it back up (just had a F1 break, good result for Hamilton, though Alonso definitely has the edge now)