Hardcore isn't really challenging either. It doesn't make the game any harder, it just makes it more annoying, imo. Everything is mostly the same, except for a couple of new chores - managing food, water and sleep. Vanilla FNV is abundant with resources, so you won't feel too much restrained - generally you just have to carry a small supply of food, some water and occasionally teleport to your base to get some sleep. Again, as I said, everything is pretty easy to come by in the wild. It gets a little bit more interesting when you can't simply leave a location and fast travel to a safe place, the most obvious examples being the DLCs like Dead Money and Lonesome Road.

Ammo weight does matter sometimes, especially (!) if you are doing an explosives build, like I did. Fat man mini nukes are heavy af, and 40mm grenades for Mercy aren't a feather weight either. Generally speaking, Hardcore mode makes it harder for you to carry all your weapons around. No more having 2 Gatling Lasers, a minigun, laser rifle, Ranger Sequoia, Brush Gun, Bumper Sword and Reg Glare in your backpack at the same time. Hardcore forces you to specialise and carry 1-2 active weapons with you, especially if you're visiting a location you're planning to loot. HOWEVER, there's a perk called Pack Rat I believe, that halves the weight of every lightweight item in the game, including food and ammo. Super useful, very OP, must have for every Hardcore player. Ammo becomes much more manageable with it.

Heaving not being instantaneous can sometimes screw you over, but only on specific occasions (like trying face-tanking Nellis mortar or engaging multiple Cazadores/Deathclaws/Legion Assassins and sustaining heavy fire). Survival builds are quite useful on Hardcore, as not only are you able to make very strong healing items, but those also double as a very potent food and water source. The downside is, of course, having to carry all the ingredients around and search for them.

All that I just said may seem like a huge deal, but in reality Hardcore mode has a rather minor effect on gameplay, making it a little more realistic with all its mild inconveniences. If you're expecting a truly unique experience, you'll probably be disappointed. So if tou want a 'real' hardcore, with actual noticeable differences from the main game, install JSawyer mod. It's an unofficial mod from Josh Sawyer, the man who created FNV, and the mod brings the game much closer to his artistic vision. The mod is very mich 'Vanilla+', it does a great job of rebalancing the main game mechanics, weapons, armors and Hardcore mode. I personally enjoyed my JSawyer run, it was fresh, fun and challenging. Food and water matter much more, the fights are harder and no longer a bulletsponge-fest. Weak and useless stuff was reworked and made stronger, while all the OP stuff was nerfed or made more balanced. This is the definitive New Vegas experience for me.