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.
Accidental Innuendo: Penny's father declares that he has "altered" Bolt. To "alter" an animal can also be a euphemism for neutering it.
All Animation Is Disney: Inverted, as many people mistake this for a Pixar film. In this case partly because after Sanders left the project, Disney brought in Pixar director John Lasseter, who influenced the film heavily in his own style.
Crowning Music of Awesome: "I Thought I Lost You" is an upbeat Heartland tune that plays during the end credits, and is performed by the two main actors. It was nominated for a Golden Globe award!
Crowning Moment of Heartwarming: Several. One of them can be Bolt and Rhino freeing Mittens from the local animal shelter, tempered by Bolt's realization that he doesn't have any superpowers to break her out with.
Bolt: "Are you ready for this?" Mittens: "No." Bolt: "...Me neither."
Fridge Brilliance: When Penny tells Bolt to "zoom-zoom" as they're fleeing the fire, Penny coughs uncontrollably while Bolt seems unaffected. Smoke rises, and Penny's much taller than Bolt, so is inhaling much more of it.
Fridge Horror: This movie has lots of it, but the in-universe studio takes the cake. Its Enforced Method Acting is deceptive, manipulative, and evidently places a huge burden of emotional distress on Bolt, even before he escapes while still thinking he has super powers. Given that this is all done merely to make his performance seem more convincing, it borders on animal abuse. And then there's the ridiculously unsafe set design; torches that use real fire (instead of the fake fire they use at some restaurants) surrounding a pad below a little girl who's literally tied up? Even if they didn't expect the dog to end up knocking over the torches, they couldn't be certain the torches WOULDN'T get knocked over, making it still indefensibly unsafe. Either the set designers Didn't Think This Through, or they thought having slightly more convincing fire was worth risking the life of a little girl over.
To top it all off the movie ends without resolving any of this. Bolt is still airing and it's never suggested that our antagonists are fired or learn anything. This is bad news for the new dog/girl hire.
Arguably, they very well could have replaced the entire production staff, which would explain the show taking such a drastic turn of direction.
Really, Bolt was a danger to himself and others when he thought the show was real. He could easily have been killed many times when he tried to jump over things, stood in front of cars expecting not to get hurt and jumped out of trucks. He also thought all cats were evil and thought nothing of holding Mittens above a road full of cars to get information.
Mittens was able to rescue Rhino when he attempted a Heroic Sacrifice during the burning studio scene by unscrewing the exit cover and taking him out before he was crushed by the debris he was trying to hold up with the hamster ball. Had the cover exit been positioned from the inside of the burning building or beneath Rhino's feet, Rhino would have performed a genuine Heroic Sacrifice while his friends was unable to rescue him from being crushed to death.
When Mittens reveals her past to Bolt. Her tone is pretty heart-breaking...
Mittens: "[Humans] pretend they're going to always be there for you, and then one day they pack up and move away and take their 'love' with them, and leave their declawed cat to fend for herself! They... leave her... Wondering... what she did wrong..."
There's a Fridge Horror element to this as well (or Fridge Tear Jerk, if you prefer): Cats are often lost accidentally during a move, whether it's due to a feline freakout at all the upheaval, or just due to people running out of time to look for their wayward outdoor cat. So it's entirely possible that Mittens' family did love her very much and are just as heart-broken as she is at their separation, and she'll never know.
During the fire, when Bolt can't find an exit large enough for Penny, she insists he goes on. But being extremely loyal to her, Bolt chooses to curl up beside her in their potentially last moments. They make it, of course. But his dedication to the very end was indeed a big Tear Jerker.
Ugly Cute: Mittens, to a certain degree. She's a skinny cat humans would look on as a stray, after all. Surprisingly, it is also deconstructed: Since she's not cute in a conventional way, because she's half-starved from being declawed and unable to hunt, humans just tend to scare her away instead of giving her some food, and she's aware that the possibilities of being adopted after falling into a pound are extremely limited for her.
The Woobie: Both Bolt and Mittens can count as this.