I was one of the people that was very critical of Fallout 4 for a great number of reasons, one of which including the game had no Hardcore Mode. Bethesda has overhauled Survival Mode to incorporate a newly designed Hardcore Mode. You can get it now on Steam by opting into the beta. From my experience, it is definitely worth a look if you were like me and loved Hardcore Mode. Here's the details:

• Saving; manual and quick saving is disabled. If you want to save, you need to sleep in a bed or other location where you can sleep.
  • There is a mod that re-enables manual and quick saving on Survival Mode for those who think this is too harsh.
• Increased Lethality; you take and deal increased damage.
• Fast Travel; is disabled.
  • There is a mod that re-enables fast travel on Survival Mode. Useful for those who have time constraints or don't want to deal with this aspect.
• Weighted Ammo; ammo has weight based on the caliber type. For example, 10mm rounds are lighter than .38 rounds. Mini-Nukes and Fusion Cores are especially heavy.
• Compass; Locations of interest appear on your compass only when you are in much closer proximity than on other difficulty modes. Enemies will not appear on your compass at all.
• Adrenaline Perk Reworked; on Survival Mode the perk is automatically granted. It confers additional player damage dealt based on its level. You can not invest skill points into it. Instead, it ranks up by the player getting kills. Sleeping for more than one hour will decrease your Adrenaline rank.
• Survival; The player is required to eat, drink and sleep regularly. If the player does not do so on time, maximum health will start to decrease, SPECIAL stats start to decrease, will lower immune system (new concept), will add fatigue (new concept) and eventually start damaging the player.
• Immune system; Similar to The Elder Scrolls, the player can now get an illness on Survival Mode. There is an immune system that prevents the player from getting an illness. Eating uncooked foods, drinking radiated or unpurified liquids, getting attacked by disease ridden enemies such as Ghouls or using harmful chems will all lower your immune system, increasing risk of getting an illness (which are most often different types of stat debuffs).
• Illness; getting an illness can often only be removed by purchasing or crafting antibiotics and using them.
• Fatigue; the player will get fatigued by exploring the wasteland and being in combat. Similar to how radiation decreases maximum health, fatigue decreases maximum AP. Fatigue can be removed by sleeping.
• Sleeping; various sleeping places have different effects. Basically, the better the quality of the sleeping place, the longer the player can stay asleep. A comfortable bed will allow the player to sleep longer in it than a sleeping bag for instance. Thus, some places are better for sleep than others (because some cannot provide good night's rest and other benefits associated with a long sleep).
• Crippled Limbs; will stay crippled on Survival Mode until a stimpack is used. Contrary to other difficulties where the cripple is automatically healed after some time.
• Encumbrance; being over the equip load will now reduce your endurance and agility and could even damage your legs and health.
• Companions; similar to crippled limbs, companions will not automatically heal after some time. If the player leaves them while they are hurt, they will be dismissed to their home location.
• Re-population; re-population of enemies and loot will take much longer than normal.

I'm having fun with it. I am desperately waiting for a mod to remove companions from not healing though, in some form. 90% of your healing items will go to your companions otherwise (because they are dumb), which seems very imbalanced. Otherwise, this is really cool. Much more stuff than I expected. I especially like the no fast travel thing.

Only thing I really have an issue with is the saves, and that's primarily because it's a Bethesda game, and they're certain to collapse under their own weight at random forcing you to reload your last save. I'd be a fan of the no-fast-travel thing if there was a car like in Fallout 2 and Tactics.

In general I think New Vegas hit a sweet spot for its hardcore mode, but there are some mechanics listed here I'm interested to see.

This is way more interesting than I expected. Adding in a risk/reward with "adrenaline" throws a nice kink in to what otherwise looks like a pretty punishing set of rules. And the save system means you're basically playing a rogue-like (or rogue-lite if you must) every time you go out to scavenge or do a mission. Hope it comes to PS4 in a timely manner.

This mode is really cool and has rekindled my interest in the game. I had fallen off pretty hard after getting maybe three quarters through the game (hard to tell exactly). It reminds me a lot more of Stalker now :)

My character build has changed dramatically, it felt like it didn't really matter what way you specced before as there was no real challenge. Perks like lead belly and action boy are really useful in the early game now. Sneaking is also great! Trying to go blow for blow with a group of enemies is a great way to get murdered now so I find myself sneaking way more.

No fast travel/reduced radar is also a great addition, I have discovered so many more places this time that I completely missed before, like the mall entirely run by Mr Handys or Vault 81. You end up criss crossing the starting area so many times that you find a lot more locations.

All in all I think it's really good. I thought it was ok/good before but I've been a sucker for Fallout since the original. But this mode makes it great for me. If you like Stalker or just want a slow paced exploration rogue-lite I would heartily recommend it.