Foremost, (like FO3) it lacks the series' combat mechanics. It's not turn based. It's not 3D-isometric. Its skills are mostly threshold (instead of percentile) based. This means that the PC is guaranteed to succeed, or guaranteed to fail.
Skills like lockpick are manual actions of the player, and can be gamed; just like the shooting mechanics... and so neither of these hinges on the character's own personal abilities. The reverse is true: The player can fail where the skilled character should have succeeded.
They can break all of their lock picks by ineptness... yet the skilled PC would never break a lock pick. Lock-picks don't break (unless horribly abused)—bobby-pins don't break either. In Fallout you didn't even NEED lock picks, they just helped greatly; it was a mechanic of the games that tools aided skill checks; not enabled them*. If you didn't have a lock pick, you used anything handy; like a bobby pin, or a spring, or anything suitable.
The whole point of the lock pick minigame is player agency—when there should be none. Player agency in an RPG is to develop the character to handle certain situations...the ones they are skilled in. Handing it over to the player for direct input is taking it away from the character, and having the player do it. Think about the player doing what the character's skill is supposed to decide.
Crippling injuries. Fallout made the ability to correct crippling injuries a character development path. First Aid didn't cut it, the PC had to
BE a doctor, or go find one. FO3 and NV allow the character to fix concussions and broken limbs with an injection, and the medical skill magically improves the effect of drugs.
Lastly... it
HAS ironsights. Throughout the Fallout series—until FO3, it has always been that the character attacks the selected target—personally. They aim, and they use their skills and aptitude to do it—and they can fail. The difference between a critical hit, and a knick, is the character's aim, but the later games all use the player's own aiming and timing to make the attacks. This means that knick & scratch wounds that the player makes at point blank with the gun centered on the target's head appear ludicrous. They are aiming better than the character is capable of; shooting faster than the character is capable of... And this works in reverse too. The skilled character can miss their shot because the player didn't point the barrel at the target.
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Peeves: NV prevents map-travel when overloaded or crippled... this is the most useful time in the game to ever use map travel—and you can't.
Wild Wasteland is an optional trait instead of being the world as it is; and so it actually costs a personal trait to opt-in. In Fallout, the world outside civilization was a scary place (more so than inside settlements). Because you really couldn't know what to expect.
