These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Base Breaker: The Chipettes, actually. People who originally grew up with the 1980s series are pretty much used to them, though people who originally grew up with the original Chipmunks from 1958 through The Alvin Show and even up to 'A Chipmunk Christmas, however, aren't so fond of them.
Dave Seville to a lesser extent. He's either a kind hearted man who loves his family but gives them tough love or an annoying father who treats them like garbage. The above parody (See Alternate Character Interpretation) hasn't helped this.
The Chipmunks' transition from human-sized furries to realistic actual-size chipmunks fits here too, despite the overrated box office results.
Foamy could be considered an angry, opinionated, underground version of Alvin.
Crowning Music of Awesome: Many people consider cover songs better than the original songs. Most YouTube videos of them will have people stating that or how their cover of it made people like the original song in the comments.
Face of the Band: Subverted. While Alvin gets a lot of attention, is the lead vocals on almost every song they have, is the star of the show, and was #44 on TV Guide's list of top 50 best cartoon characters of all time, Simon and Theodore are anything but forgotten or put in the background. Each of them have their special and memorable moments in the spotlight, each have their own fanbases, and all three of them share balanced screen time. Change anything, and it would not be the same.
Fan Community Nickname: Some fans call themselves "Chipaholics," though there really isn't (so far) an actual community nickname for the fandom.
Crack Pairing / Broken Base: There is a serious divide among the fandom with canon shippers and mixed shippers, it occasionally even grows to a point where the two groups of shippers practically go to war over why their respective shipping is better, and why the opposing shipping sucks.
Speaking of phases, the crack pairings go through many different phases among the fandom, which almost always ensures a string of fluff fanfics from different authors. Popular phases over the years have included pairing Alvin with Eleanor, Simon with Brittany, Dave with Vinny, and even Alvin with Simon, however, none of them have quite put the "crack" in "crack pairing" as much as Dave and Brittany, with even a few fanfics involving Dave impregnanting Brittany.
Self-Fanservice: This is also very evident in fandom, if one were to ever browse through Fan Fiction.Net or deviantART. This is especially true of The Chipettes, moreso than The Chipmunks (though, that's not to say the boys don't have their own fair share). In the case of fan art, many fans age up The Chipettes considerably, giving them an excuse to be drawn with boobs and Hartman Hips. Eleanor, in particular, is drawn much slimmer than she's usually depicted in the franchise, and also has a tendancy to be glammed up as well, especially when she's paired with Alvin in the fan work. Brittany also gets glammed a lot, though it's usually more because of how she's already quite a fashionista, and in the case of fanfics, Brittany Really Gets Around, with just about everybody (even her own sisters). Jeanette's fan art usually tends to be just a tad more tasteful, for the most part, but however, fanfiction is an entirely different story: either she's a depraved horndog dying to have one of the boys (mostly Simon) inside her (or even play with Brittany), or a constant rape victim. It also doesn't help that often in fanfiction, the girls' physical appearances and maturity are almost-always explained in very detailed descriptions.
Ensemble Darkhorse: Both Vinny and Uncle Harry seem to get quite a bit of attention from the fandom; the latter seems to stem from the similarities between Harry and "Uncle" Ian from the live-action/CGI films.
"Funny Aneurysm" Moment: In "Thinking Cap Trap", the Chipmunks and Dave appear on a game show. When asked to identify the Bronx Bombers, one of their opponents said they were a New York terrorist group instead of the New York Yankees. This lost its hilarity for obvious reasons after 9/11.
Love It or Hate It: This has increased among much of the Chipmunk fandom in recent years. A large majority of the fan base grew up with this particular series and love it, especially for nostalgia. On the other hand, some fans hate for one of either two reasons, because it focused less on the music (unlike The Alvin Show), or they're sick of Bagdasarian Productions releasing the same handful of episodes on DVD over and over again.
Seasonal Rot: During the DiC era of the series, the stories, as well as the overall production, slowly, yet steadily, grew weaker and weaker, compared to the quality of the earlier, Ruby-Spears era.
Critical Dissonance: Seriously, people had nicer things to say about Transformers: Revenge of the Fallen. For this movie, it didn't do very well with the critics in the first place, but at least some of them liked it. The reaction was the same for the sequel. But by the time the third one came out, it became almost unanimous that the series had outstayed its welcome.
To clarify, the third movie did horribly with the critics but was among the highest-grossing films at the time. The critics were quick to make insinuations on what kind of person would actually like such a movie, as reflected in the Rotten Tomatoes consensus:
"Lazy, rote and grating, Chipwrecked is the Lowest Common Denominator family entertainment that is strictly for the very, very, very young at heart."
Tainted by the Preview: Some fans who grew up on the 80's cartoon did not gravitate towards the eponymous Chipmunks looking more chipmunk than humanoid, and fans in general were not amused by the poop-eating gag shown in the trailer. Much to the latter's relief, the movie only really had two instances of toilet-humor.
WTH, Casting Agency?: Some felt this way about Justin Long getting cast as the voice of Alvin, since the inevitable voice modulation would make his voice unrecognizable.
Just Justin? What about all the chipmunks?
Doubles as Executive Meddling, as Ross Bagdasarian, Jr. and Janice Karman were originally going to voice the Chipmunks (just like in the cartoons) but the studio insisted celebrity actors do the rolls. At least the original duo provide the singing voices. In fact, only Simon has a new singing voice compared to the cartoons.
For The Squeakquel:
Big Lipped Alligator Moment: Digger the Gopher (as voiced by Eric Bauza) cameo in the second movie. There's no build-up to him he just appears as a Deus Ex Machina during the climax. Most people don't even know who he is (he's a mascot for NASCAR Racing).
Moral Event Horizon: In the second movie, Ian crosses it when he threatens to barbecue the Chipettes if they don't do what he says. After doing this, it's almost difficult to accept the Enemy Mine situation with him in the next movie.
Squick: Alvin flirts with some human girls. High school girls. Think about it, then take a long shower.
The Chipettes having more feminine bodies in the movies. In the show they were in Elementary School!
Their first appearance has them naked. The dance scene that follows is kinda creepy.
The Chipmunks attempting to cover up what's happened to Dave's aunt by stating she's taken up pole-dancing.
We're Still Relevant, Dammit: The movie saw the Chipmunks attending high school (and behaving as such), singing mostly modern pop tunes, and spouting lines from such films as "Silence Of The Lambs" It ultimately wound up crossing over with...
What an Idiot: Had Ian played his cards right and learned from the mistakeshemade in the first movie, not only would the Chipettes have remained on his side, but he would have most likely won out in the end.
Sequelitis: May or may not have happened with Chipwrecked, which received mostly negative reviews and even David Cross went on the record of saying that just the making of the movie was the most unpleasant experience he'd ever had.
Actually, what Cross meant by that was that the directors made him wear a hot, stuffy pelican suit on a cruise ship for a week instead of using a double (because for the first half of the movie, you can't see who is inside it). He didn't mean the whole movie itself.
Well, he did basically call Janice Karman Hitler in an interview. He didn't outright name Janice, however, he did specifically refer to, "A certain female producer", and since Karman and Ross Bagdasarian, Jr. were the producers of the movies...