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.
Complete Monster: Piella bamboozles Wallace into falling in love with her solely so she can then murder him out of an intense hatred towards bakers, whom she blames for her massive weight gain. Bear in mind that she's already succeeded twelve times over when she meets our heroes — in other words, she's crossed the Moral Event Horizonbefore the first scene, in which she murders her latest victim. That's not even mentioning her abuse of poor Fluffles, or how she falsely accuses Gromit of attacking her in order to make Wallace distrust him. In short, she's the darkest villain yet in this series, and she dies without any hint of remorse or redemption.
On the other hand... Her last scene is her thin self as a ghost waving goodbye to Wallace and ascending to Heaven, implying either that there may have been some level of redemption to grant her access to Heaven, or that Wallace, ever the Cloudcuckoolander, is hallucinating.
Growing the Beard: A Grand Day Out isn't necessarily bad, but it's far more Surreal than the later episodes, Wallace's only invention is the rocket, and the bad guy is a... living oven. With The Wrong Trousers, Wallace became far more of a tinkerer, Gromit became the archetypal Silent Snarker and the series received a massive Animation Bump.
Karma Houdini: Wendolene in her poaching sheep to get free yarn. In fact she expresses no suprise as her robot dog is killing sheep en masse to make dog food.
Fluffles is also implied to have been assisting Piella murder at least a dozen bakers. Both examples are shown to be rather remorseful however, unwillingly dragged into the act by the much more callous Big Bad, and eventually draw the line after it goes too far.
Wendolene: I want no more of this rustling! It wasn't so bad when it was just the wool but, this is evil!
Wendolene didn't exactly get away without a punishment if you consider the fact that Preston actually tried to kill her and ground her up into dog food when she finally tried to stop him.
Moral Event Horizon: During his malfunctioning, Preston attempts to turn Wendolene and the sheep into DOG MEAT!!! Surely that qualifies.
Lord Victor Quartermaine is willing to kill the Were-Rabbit (even though he knows it's really Wallace) just so he can marry Tottington for her fortune.
Tear Jerker: When Gromit runs away from home in Wrong Trousers and when Gromit cries over Wallace's apparently dead body in 'Were-Rabbit.
Another example is in "A Close Shave." In the last newspaper with the headline of Gromit going to jail for life that Wallace and Shaun are reading, both have tears in their eyes, as do several other sheep reading with Wallace and Shaun, as Wallace says, "Oh, Gromit," before he and the sheep look at a portrait of the two together.
The Woobie: Gromit, particularly in Wrong Trousers. Fluffles also qualifies up until the end of Loaf and Death.
Fluffles is probably the most Woobie character in the franchise. Piella hit her and you could literally hear her yelping in pain! It is also vaguely implied that she has suffered this abuse for quite a while
Wallace at the end of A Close Shave. After everything that they had gone through up to that point to earn their happy ending, Wallace finds out that Wendolene is allergic to cheese and can't stand it at all.