I just want to respond with the episodes you said were some of the best of later day Family Guy. Though North by North Quahog and Petergeist were good, the rest I find practically unwatchable. Road to Germany was trying to be novel in the whole Stewie/Brian going on a road trip yes but there was a point in the episode where it was a blatant calling out of the McCain campaign (since the episode originally aired in 2008 when we were actually supposed to care about the guy) comparing them to Nazis by having one of the Nazi's Stewie and Brian find having a McCain/Palin button. Though I'm wasn't and not a supporter of him in anyway and I might have found it edgy when I was 13 when the episode aired, looking back now, I find it really culturally irrelevant and dated whatever political view might stand.
Next one, Brian & Stewie was just awful. It was basically the episode that made me stop watching Family Guy regularly. (Considering, with a few exceptions, I hadn't enjoyed it since the 100th episode special) I remember the hype about this one being that it was going to really flesh out the characters and have none of the usual tropes that Family Guy is synonymous with and I was curiously intrigued. But what showed was little more than a really bad take on The Breakfast Club and that's being nice. Sure The Breakfast Club still somewhat holds up to Gen-Xers, mostly for it 80's nostalgia and teens talking about their family issues but Brian & Stewie had none of that. From what I can remember, it was them admitting that they loved each other and Brian cleaning out Stewie diapers and poop before they get really weary and realize that the door was open the entire time. Ignoring that that kind of an ending is an unfathomable cop-out, the entire episode just was a poor excuse to try and add more depth to the characters resulting in making them even more unlikeable than before. Three Kings was passable at best but not memorable in the least say unlike Petergeist or North by North Quahog. To be honest I never have seen ...And Then There Were Fewer so I can't discuss its faults rather than assuming that it has some.
And for Partial Terms of Endearment, just pathetic. Yes you could say that they tried to be edgy dealing with a really hot button topic but they way they did it just seemed that they really were going for shock value and leaving funny out of the episode or trying to bring the Family Guy formula of cut-aways, obscure pop-culture references and college aged stoner/gross-out humor to a topic that it really doesn't mesh or mesh well with. (see politics & Family Guy as well) Also it must be added that the episode never or has never aired on TV where most people watch Family Guy (in rerun form) thus limiting the effect it can have. Yea sure it did ultimately did take a stand on the issue, an stand that I personally agree with, but the way they did it was really vain to say the least. They had the serious Lois monologue at the end which was leaving it ambiguous, which I was surprised with and thought that they were actually going to leave it up to the viewers to come to their own conclusions on the route they took which I thought would have been the best way to handle the ending since people of both sides could fantasize about the option they took as seeing eye to eye with the personal philosophy about the matter at hand. But they did decide to stick firm to their stand which others could see as noble as standing up for what they believe in and not giving into pressure, but the way they said it was unforgivable and cowardly to say the best. Just having Peter blurt out after the monologue saying they aborted it at the very end was probably the worst way they could have dealt with the issue. It showed a sign of cowardice towards the issue since throughout the episode, they didn't take a decisive side and the point was to try and show both sides of the issue but the stand they showed at the very end had no previous backing (say for Family Guy being a usually left/liberal show) from the episode and it seems that they were so scared of saying their stance throughout the episode that they decided to blurt it out at the very end leaving no logical steps in how they came to their conclusion.
Now there are some good post 100th episode episodes I like (such as Tales of A Third Grade Nothing, Episode 420 in some respects, and Road to the Multiverse along with their take on the original Star Wars Trilogy) and I think that the previously stated Family Guy formula (cut-aways, pop culture references, & raunchy/crass humor) works best for parodying movies and character development in their original molds [see the first 3 seasons] and the formula can work when they do try to go for controversial topics [see You May Now Kiss The Guy Who ...Uh Receives, Hell Comes to Quahog, Prick Up Your Ears, Boys Do Cry, and Episode 420 in some respects again]. But I do think that the first 5 seasons were the best and do now wish they would have gracefully ended the show with the 100th episode rather than seeing it morph into what it's become now, say for the few previously mentioned exceptions, and I don't say that as a guy who experienced the first 3 seasons as a 18 year old frat boy but as an 11 year old when I first watched it. Even when I was watching the 6th-8th seasons live going through puberty, I couldn't help but notice that much of the original Family Guy formula was thrown out and the parts that remained were ramped up extensively to make it more bloated without realizing that the parts of the original formula the writers threw out where what made it work in the first place and the ramped up remains couldn't tread water without a serious overhaul that lost what Family Guy originally was.
I also see the characters changes as negative. Peter being deemed mentally retarded, which they tried to downplay for the 4th and 5th season until they remembered they said that when they were scripting most of season 6 and onward to this very day. Lois as the subtly violent housewife to the raunchy housewife who, if she were really as smart as she comes off in later seasons, would leave Peter in a heartbeat. Chris as relatively unchanged. (which is for the best) Meg as a somewhat smart uglyish looking individual that can be relateable to just a punching bag. Stewie from a smart, calculated little genius (yes the matricide did eventually get old and they put that to rest in the 100th episode) to a constant gay joke, losing much of his original genius. And Brian who started out as the smartest of the dumb bunch but has morphed into a left/liberal douchebag (not to say that liberals are douchebags but Brian's specific characteristics/mannerisms fueled by his latent rampant left ego) who could be seen as a rallying point to liberals and a parody and joke/accusation to right/conservatives. But the overarching character development of the show is time for another rant and I'm just about out of fuel now. Thank you anyone who read this entire thing and if you want, respond. I'm always game for discussing Family Guy. Cheers.