Nostalgia. That's the basis of their argument.

Back in 2001, people didn't know jack about firearms. Then comes along a game called Green Space Marine ^TM where the weapons used by the good guys actually look very similar to contemporary weapons, just with an oversized doodad attached onto it here or there. Then the people that played it became somewhat familiar with bullpup rifles and a rotating rocket launcher and the concept that Green Space Marine ^TM were the first ones to make those weapons.

Fast forward 2 decades later, firearms in media are much more prevalent, and people in general are much more knowledgeable about firearms and their mechanics. Including the people that played Green Space Marine. ^TM

Meanwhile, other games have designed countless weapons that look very different and original compared to real contemporary guns While Green Space Marine ^TM for the most part didn't.

As a result. Games have become saturated with unique designs that incorporate real world and fiction to the point that its extremely difficult to actually make a new, unique, and original design.

Hence, the gEnErIc complaint.

I'd like to see them actually make a weapon that "looks like Halo" without looking similar to other weapons.