But you're facing the same enemies from the same direction with the same resources.
Assuming that you want to get anything done, you will always have to face the same enemies open world or not.
Unless the game is composed exclusively of straight hallways (very poor linear level design), then there's always more than a couple directions of attack. You may enter and exit the level from the same door, but there's about as much room for finesse once inside.
If players stay in a rut, it is because they like it there.
And my point is that's bad. The player should feel comfortable to a degree, but if they're completely complacent, then I don't believe the game is doing it's job.
Maybe I'm too idealistic, but I believe that good art needs to inspire thought and should challenge at least one aspect of people's existence whether it be their morals, their mind, or their skills. Incidentally, games can do all of those things quite well, and I think that most games should try to engage players to the best extent they can.
The only way the linear design you describe would work in a rules-based RPG (as opposed to a straight-up action game) is if the ruleset were particularly robust, and we just don't see that a lot in digital games.
Says the person who doesn't play many action games. Complex rulesets aren't necessary, just good AI, good level design, and a decent assortment of tools.
There are many ways for me to approach combat in ME3, for example, but none of them are particularly subversive. But both DAI and Skyrim allow exactly that, intended or not.
You found a way to play despite the limitations. I'm sure you did that by using the limited tools available to you and formulating a plan to adapt. It may not seem particularly subversive, but that's the beauty of limitations.
I basically don't play action games (unless I can subvert them to eliminate the action elements), so that narrows the field considerably.
They force us to play the game, which isn't what I want to do. I want to play in their game, and I want as many tools as possible with which to do that. I'll use exploits, and mods, and the developer console, and pretty soon the thing I'm doing might not resemble the developers' intent even vaguely.
Then my question is: why play Mass Effect? I respect the fact that you don't like action games, but why cling to a series that is fundamentally different from your ideal game? Mass Effect isn't a simulator. It's a game that intentionally puts you in the shoes of a fighter and intentionally challenges the your skills.