He sounds very embarrassed on the commentary to Cartoon Allstars, mainly because he felt like the Critic was nowhere near his now-usual pathetic characterization and sounded more angry and threatening.
In the voiceovered-after-said-episode commentary of "The Review Must Go On", Doug said that he hates the Timothy Green episode. Commence eye-rolling, kids.
He's also ashamed of Signs, feeling like it only worked because of the aliens conversation and realizing while editing that everyone would call him out for trying too hard to please the "we only want rage" crowd with the Freak Out.
While he still thinks the review was funny, Doug felt the sketches in the Catwoman review were too disconnected from the review itself.
In a weird example of the backlash coming before the video in audience eyes, at a Youmacon panel Doug was squirming about how bitter and offensive he got in the Reloaded reviews of the anniversary movies, and used the script as scrap paper for a scene in Demo Reel.
Creator Breakdown: "The Review Must Go On" invokes this when the Critic tells Doug that he wasn't really ready to end the show, he just got burned out from doing an episode every week alongside convention appearances, anniversary specials, and his normal day-to-day life. If this is the reality or not is hard to judge, given that the video is obviously dramatizing the real life events.
Ironically, "The Review Must Go On" was the result of a lot of bitterness towards the fans. Doug admitted on his commentary that Rob had to rewrite a lot of it because it was even nastier and filled with plot errors, and "Donnie = Critic" was only because they were so tired of demands to bring Critic back.
Leslie Nielsen Syndrome: Rachel and Malcolm started on Demo Reel, a show that placed more importance on drama than comedy, but "do what they're told" on Critic and ham it up in whatever skits they're given.
One of Us: As evident in the editorial "Why is Loki So Hot?", where he reads word-for-word this wiki's definition of The Woobie and is surprised that he is listed as well (although as a Jerkass Woobie instead of a regular one).
In The Cat in the Hat commentary, Doug mentions that he has read the Heartwarming page for the Nostalgia Critic.
Rule34 — Creator Reactions: Doug enjoys the fic, brings it up a lot and has made fun of the people who expect him to be freaked out by the slash and some of the more... extreme things he and his characters have been put through. And Rob finds it all hilarious, as most big brothers would.
Taken a step further at 2012 Shadocon, where he states his full support for all the shipping and teases that he and his characters are always the ones submitting.
Trolling Creator: All the hyping build-up to Critic heroically saving the Avatar franchise comes to nothing in the actual review. Sokka and Katara realize they've got the wrong person, he keeps running away, Amon bends out “what's left of” his talent, Doug manages to slam him in-universe, the “only one show” speech doesn't work and it's Aang who saves the day.
In the first showdown between the Crtitic and the Nerd, it's revealed in outtakes that the line "That's the fuckest thing I've ever heard, shit mop" was originally going to be "That's the fuckin' weirdest thing I've ever heard, shit moth", but Doug flubbed the line and decided he liked it that way.
Much of the Earthbender rant in The Last Airbender review was improvised according to the commentary.
Type Casting: Rachel gets fanservicey stereotypes of women, and apart from the devil, Malcolm gets pathetic characters. Acknowledged by Doug in the Turbo commentary.
Doug: That seems to be the running thing. Whenever I write something for Rachel, she just acts crazy. Whenever I write something for Malcolm, he is just somebody's bitch."
What Could Have Been: There were several movies, that the Critic was scheduled to review, but no videos were made for various reasons.
There was originally going to be an Old vs. New of The War of the Worlds, but it was held up due to the controversy with The Room. Eventually it was dropped, because Walker found both movies too underwhelming and overrated to compare.
Drop Zone was dropped and replaced with Ernest Scared Stupid, because the Critic decided to take the opportunity of spending the whole October of 2010 talking about horror movies.
Walker wanted to review Matilda because he hates it so much (It was #3 on "Doug's Top 10 Movies He Hates But Everyone Else Loves"), but so much backlash from his audience caused him to scrap the review. The later cameo appear of THE Mara Wilson, and her subsequent appearances in more Channel Awesome videos, have made up for the loss.
After the disastrous reaction to Let's Play Bart's Nightmare, the review of James and the Giant Peach was supposed to open with an argument between the Critic and Douchey McNitpick, which would basically have been a massive Take That against those who complained. Doug was talked out of it by others, who persuaded him that in the best case it would look like he didn't understand why the video was so disliked, and in the worst-case (and probably more likely) scenario he would wind up destroying his fanbase overnight.
The Follow That Bird review was originally meant to be a straightforward Nostalgia Critic episode — until Doug watched it to get ready for the review and realized he couldn't make fun of it. He wound up writing in Chester A. Bum to take over the review after the Critic broke down, and the review itself became 5 minutes long!
The sexual harrassment Running Gag in Dawn Of The Commercials could have been worse, as Doug wanted Rachel to fondle him at the end of their bit and Jim said "So you're going to be on your knees touching Doug".