The good thing about crysis in respect to buying weapons is that you don't really need to buy any weapons, just a couple of accessories and the nukes to actually win the game. If I'm trying to save points I'll just buy a pistol silencer and a grenade and sneak around, kill someone (often with a strength punch) and nick their weapon. You aren't hugely disadvantaged for having no weapons.
On the down side I think in some cases it's too difficult to escape once someone has started firing at you, specially if you're out in the huge open space that the PS maps provide. If you're on armour mode and start getting shot at, you can't speed boost away or cloak because you've lost all your energy on armour. It often comes down to first-person-to-shoot-wins. Then once you die you have to travel all the way from a spawn. A lot of my PS play so far has been driving around punctuated by a few kills and captures here and there. Was playing beach yesterday and it was mostly a case of drive to energy site. Sit there on my own and capture, someone comes along and kills me (or I kill them). I drive back to the energy site, repeat.