I think the issue is what people are looking for in a game. There's realism to consider. It's not realistic that I'm going to run around with the entire Doom arsenal on me without serious injury or death. Or at least moving reeeeally slow. There's also the notion of choices having impact.
If you can carry one of every weapon in the game, an entire dimension of choice is eliminated. Instead of having to choose the two or three weapons that best fit your style, or that you feel best fit the situation at hand, you essentially have
one weapon with
ten models. You're carrying the ultra-Swiss-army-gun. Sure, you have to "choose" whether to fire bullets or rockets at the target, but that choice is a simple matter of pushing a button.
When you're given a limited inventory of weapons, you have to make decisions
and then live with those decisions. I like the close-ranged punch of shotguns, and I like the reach of my sniper rifle... but both weapons mean I've got to deal with lengthy reload times or pauses between shots. If I take both, I have to live with that downside. If I choose a weapon with a higher rate of fire in place of one of them, I'm making a trade in something else (reach or close-range power).
There are reasons for limiting inventory, that's the take-away here. In some situations, it's not as big a deal. I'd argue that, for Duke Nukem, it's an inconvenience that isn't necessary in a zany, farcical blast-fest. At the very least, a two-weapon limit is hilariously low for Duke. But in games that are survival-oriented, squad-oriented, or just focusing a bit more on realism? Yeah, it's a great fit.
Treblaine said:
My point is when you have such a limited inventory you can't make any of your weapons too unique, every one of them must function "well enough" in all circumstances as you only ever have one alternative.
This is the best point you make, but it's incomplete. This is a problem of overall game design, not just the weapon inventory system they choose. If every problem has the same basic answer (throw bullets at target until it stops), then even the most "unique" of weapons will be the same thing with different animations. There are many solutions to these problems, while still maintaining the limited inventory:
1. Situational weapons don't have to pop up in incredulous ways. Maybe you have the chance to get the weapon you need from the enemies you're fighting on the way there. You get to a boss and realize you need a missile launcher, so you know to run back to that earlier spot where you downed a guard that had one. Maybe you pass a squad of other would-be heroes that got wasted on the way in, and you pilfer some of their still-working equipment. Plenty of ways to get you the weapon without breaking immersion.
2. Separate "weapons" from "tools." The gravity gun doesn't need to be thought of as a "weapon." It's mostly a tool. Not every item a person picks up in a game has to be designed specifically to kill things--that's another problem in game design. So, perhaps you can only carry two weapons, but you can also carry two
tools. They aren't directly useful in killing things, but they can help you turn a situation to your favor or solve a puzzle.
3. Secondary fire options. Instead of making each weapon separate, you can have a standard function (pistol, SMG, shotgun, rifle, etc.) and make the "unique" thing a secondary function (flamethrower, grenade launcher, shrink ray, grappling hook, whatever). Lots of games do this, but it could be improved upon. This could allow each weapon to be functional in all circumstances, but it would also have a more situational and "flavorful" use based on your personal preference.
Just a few ways that better design
in the whole game can fix the issues that you're assigning to the limited weapon inventory.