But what does gameplay you meant, here? Combat? Because combat is just an aspect of the gameplay in RPGs. Unless you're a combatfag, combat doesn't necessarily constitute the entirety of gameplay.
Yes, PS:T had crap combat mechanics, but the other aspect of gameplay such as skill checks and reactivity were absolutely top-notch, so it has good overall gameplay. You can still play PS:T for the combat and still get skill checks and reactivity, but the experience would probably felt sub-par in comparison to when you play PS:T purely for the story. But again, that doesn't necessarily means it's a game with bad gameplay, but rather it's a game with bad combat mechanics.
Saying PS:T had bad gameplay because of bad combat mechanic, is similar to saying New Vegas had bad gameplay because of its shooting mechanics is inferior to that of Fallout 4's.
Dark Souls is an Action-RPG (ARPG), since the game is action first, role-playing second. Especially since the combat mechanic of Dark Souls required ~99% of player's input (with 1% being the character's stats input, like Strength/Dexterity/Intelligence/Faith requirement for weapons/spells/miracles), so its RPG aspect is not even comparable to that of any cRPGs ever. Haven't played System Shock 2 past the tutorial, but I imagine there won't be any skill checks found in other cRPGs, so I'm going to assume it's a shooter game first, role-playing second (correct me if I'm wrong).
Honestly, I can never understand why anyone would want to play Skyrim for its vanilla combat. It's an absolute slugfest, doesn't even require any slight bits of thinking, just click-click-click if your target has no shield, or spam power-attacks against shield, or just exploit the shit AI by sitting there sneaking and shoot arrows once in a while. The first time I played Skyrim I played by exploiting back-stabs and sneak arrows, since the melee is atrocious. Now, though, having been baptized by the Fire that is Dark Souls, I can never, ever go back to Skyrim, even if I would exploit back-stabs and sneak arrows like I did once.