A couple of caveats. First, there is no doubt that Gooder is right that neither Land of the Dead nor Diary of the Dead can be particularly considered worth anyone's time. I'd consider the former entirely inessential rather than terrible, and even the latter has its moments (I also don't think it's fair to suggest that showing both sides of an argument is the same as not being sure of what one wants to say), but I'm not particularly inclined to defend them too vociferously, not when the difference of quality between those films and the ones that preceded them is so undeniable.
No, Gooder's true heresy lies in his entirely unforgivable suggestion that Day of the Dead is less impressive than it's predecessor, Dawn of the Dead.
The argument that the two films tread the same ground is superficially compelling; both involve a small group of survivors attempting to not get bitten by the hordes of zombies outside the complex they have locked themselves inside. Both contain the message that ultimately it's not the zombies we need to be worried about, but our fellow humans (though they do this in very different ways, and that particular theme is a long-established staple in disaster movies, which the ...Dead series can just about be considered to be, if one squints hard enough).
Beyond that, though, the two films are surprisingly different. If anything, Day... is the entirely logical progression of Dawn..., and for more reasons than simply being set after it (the only way in which the film can be considered a sequel beyond the zombies themselves). The former film asks how one would respond to society crumbling. The latter considers what happens once society has crumbled, past tense, and ain't never coming back. To take one example, Dawn... concludes with an attack on the protagonists' mall by a gang of anarchic bikers. By this point of the dead's inexorable replacement of the living, one still needs to be concerned about looters.
It would never occur to the survivors trapped inside the bunkers of Day... that they might need to guard against looters. The hordes of zombies have become an impenetrable ocean, all that the exhausted humans can see in any direction. Whilst Dawn... chronicles our fall, Day... kicks off by asking... what now? The stress of surviving Dawn... drives Peter to within inches of committing suicide out of sheer despair. Almost every character in Day... starts out that horribly damaged.
Much has been made, and I think fairly, of Dawn...'s indictment of consumer culture. Bored? Go shopping. World ending? Go shopping. Not sure where to find delicious brains? Go shopping, and eat the shoppers. The corollary to this, though, is that the survivors use the mall as a way to block out the truth regarding their situation, in the same way anyone might use retail therapy to distract themselves from the problems in their life. Dawn..., at its core, is about fiddling whilst Rome burns.
The only fiddling the characters in Day... are doing is with zombie brains and power drills (and their own sexual organs, apparently, though the less said about that the better). Not for them the questionable delights of mannequin target practice; they have a job to do. They have to turn back the zombie invasion. What makes Day... so much bleaker and harrowing is that whilst the characters in Dawn... needed only to survive, those in Day... have been given a mission. It's a mission that is obviously, unquestionably impossible, and moreover had a strict time-limit long since expired, but they keep doing it because there is no other choice, and because if they do give up, it means genuinely accepting that the end has come and gone.
Or is there? I wrote something about Day of the Dead in the run up to Halloween last year, as part of a larger article on horror films dealing with the apocalypse, and now seems a good time to dig it out:
Strangely, then, whilst Day... is on almost every level a bleaker film than Dawn..., the central message of processing the past and letting it go is actually more optimistic than observing the gradual numbing of the characters in Dawn... (Peter's last minute change of heart notwithstanding), which manages to end the trilogy on the highest possible note one could expect without cheating the audience (well, the final helicopter nightmare is a cheat, but still).
The film concentrates on the various ways the characters (soldiers and scientists, drunks and evangelicals) process the fact that humanity's time is passed. If anything, the film is the Kubler-Ross model (denial, anger, bargaining, depression, acceptance) applied to celluloid, only the one dying isn't a person, it's a civilisation at best and a species at worst. Logan is denial, convinced that he has a way to keep humanity alive, even though it's obvious to everyone else that it cannot possibly work (how exactly he expects to millions of zombies tamed by constantly feeding them human flesh is a question best left answered, although it does feed my pet theory by being the bargaining part of the equation, "Have this food and don't eat me, please!"). Rhodes and most of his men are anger, blaming the scientists for their predicament and their losses, determined to "blow the piss" out of the enemy even though they know they don't have enough bullets, let alone men, to do the job. Salazar, fairly obviously, is depression, and for much of the film, so is Sarah. She might be more level-headed than anyone else (with the possible exception of Fisher), but she's still massively strung-out, still lamenting the loss of what she personally and humanity in general had, and terrified that what little she has left (including her lover) is about to be lost too. As the film continues though, she begins to reach acceptance, helped out by William and John, who are already there, and are determined to simply live out their lives finding what comfort they can.
In fact, Day... is an even more poignant example of the accompanying sadness I mentioned before, because it focuses on the exact moment the first type of apocalypse film (the sky is falling!) turns into the second (the sky has fallen, and we ain't getting it back up again). The characters have to make a conscious choice to let go of the hope they've held since the crisis began, and find something else to cling to instead. These films are generally about acceptance to some extent, but what makes Day... unique is that it focuses on acceptance by those who were tasked with affecting change. Viewed from this angle, the fear of losing the support of society becomes instead the fear of being forced to change, to re-write one's internal assumptions and certainties.
All of this is without mentioning the film's ace in the hole, Bub (who, to be fair, Gooder holds up as the best part). Bub exists as a sort of twisted reminder that every ending is a beginning (which Romero expands upon in Land..., with admittedly distinctly mixed results), and as the most direct demonstration yet that there are worse things in Florida than the stenches. He is also proof made (rotting) flesh that hoping the clocks will turn back is simple insanity, which of course pushes Sarah closer towards acceptance (and Rhodes closer towards a psychotic break).
There are other reasons to hold Day... up as superior to Dawn..., the acting and characterisation are better, and the zombie make-up is more disturbing (the first shambling horror we see roaming the streets of an abandoned city is possibly the best zombie yet committed to celluloid, though unsurprisingly this isn't a uniform standard throughout the film). Mainly, though, it simply feels like a more human film, even if most of the actual humans invariably behave like jerks, and/or get horribly killed, and one that has a message that feels important, rather than just snarky.