It is not a matter of expectation. DNF is bad because: ...
As I said, whether a game is thought of as good or bad is personal opinion.
Also, you clearly expected it to not have weapon carry limits, useless NPCs, etc, so as it does you dislike it, therefore it is expectation. I read up on all of these aspects of the game beforehand so that I knew what to expect, and with that in mind I played through it fine and treated it for what it is, a sci-fi shooter without the need for much thinking.
As for Serious Sam HD coming out inbetween Duke3D and DNF, the game passed between how many developers and with how many delays? The released game is not indicative of a game released at the date it was released, but one dated maybe 3 years prior. Gearbox just inherited what was there and tied it up where required in order to get it released. Don't think of DNF as a 2011 game, but instead as a 2008 game.
Anyway, enough of DNF opinion, for it to come here to GOG we'd need to get Steamworks titles showing up on here before it could be sold by GOG.
By the way, GOG now has no meaning. It used to be an acronym for Good Old Games, as in the Good Old Days, which we also know were not universally 'good' either. However, now GOG is just a name that has no meaning. The staff who post here on the forums have said so themselves.