You'll have counters that track your hunger, thirst and fatigue levels. Once they hit threshold levels (200, 400, 600 and 800) you'll suffer increasing stat penalties (plus pop-up warning messages), and if any of them reach 1,000, you'll die. But they move pretty slowly, with thirst being the one that increases most quickly and sleep increasing the slowest. One thing that I find kind of annoying with vanilla hardcoe is that you have to access your Pip Boy to view these stats, but that can be easily fixed with HUD mods (if you're on the PC).
I really like the feature of adding weight to ammo. You can't mule around a dozen weapons with thousands and thousands of rounds of ammunition for each one. You'll find yourself limiting it to a handful of favorite weapons with smaller amounts of ammo. I also really like having stimpaks heal over time. If your battle strategy involves charging at minigun-wielding enemies while spamming hot-keyed stimpaks, you'll need to come up with some new tactics, or be prepared to die. A lot.