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.
George brings his problems on himself by running an overleveraged, illiquid bank and letting his alcoholic uncle handle business.
It's not a bank, it's a building and loan. People make deposits and the money is then leant back out in the form of mortgages to the locals. They were generally considered to be one of the safest investments you could make until deregulation under Ronald Reagan.
Pottersville looks like a fun town... well, unless you're one of the poor working class whose livelihoods are destroyed.
Capra himself said he made the film in large part to "combat a modern trend towards atheism". Little wonder that its protagonist is a Christ figure in all but name.
Big Lipped Alligator Moment: Mary losing her bathrobe and having to hide naked inside a bush. George even lampshades it. "This is a very interesting situation!"
Complaining about Shows You Don't Watch: Fans didn't react favorably to the announcement of a sequel, It's a Wonderful Life: The Rest of the Story, in which George Bailey's selfish grandson learns how better the world would be if he were never born. However, the studio that announced this sequel did so under the assumption that the original movie still existed in the public domain. The current rights holder, Paramount, quickly expressed a reluctance to back the idea.
Crosses the Line Twice: that bar scene where George gets punched ... okay, he deserved it, but did the guy that did it have to insult his kids too?
Well, George did insult the guy's innocent wife, who had been badly shaken by his tirade. If a line was crossed twice, then George crossed it first.
Glurge: It tugs on the heartstrings so hard, a reviewer coined the term "Capra Corn" to refer to it. Afterwards, Frank Capra himself started using the phrase to describe his well-known sentimental film style. Some background on it all here.
The Glurge aspects were lampshaded in the first Batman: The Animated Series Christmas special, "Christmas with the Joker"—it was the reason why Bruce was initially unwilling to let Dick show him the movie. Dick points out that it's about how one man can make a difference, alluding to Batman's role in Gotham City.
The sugary aspects of it are also fairly heavily cut down by the actual movie, which is substantially different from its reputation as a slice of cheese. The sex jokes and snarkiness can surprise first-time viewers expecting nothing but the ending. And if they weren't expecting the ending, then the last quarter of the film can feel like a sudden shift to the Twilight Zone.
Harsher in Hindsight: The banks today are basically run by Potters, and the way they were run caused much of the late 2000s recession.
It runs the other way, too. Potter is indignant that Ernie get a loan simply because George sticks up for his character. While mainly just being a jerk, part of his point is doubtfulness that Ernie will ever be able to pay it back. During the 2000s, some banks gave out loans to people they knew couldn't pay them back, which has been cited as a major cause of said recession. Some of these were very Potter-esque dealings designed to screw lower class people over, but others were cases of the banks being screwed over - being cajoled into making poor decisions under the pretense of it being the right thing to do.
The difference is, George's Building and Loan was never really intended to make a profit. The 2008 mortgage crisis was caused by banks offering mortgages that they knew were worthless, and then betting on their customers to default, thereby making a tidy profit on the failure.
And often they were forced into those poor decisions by the government with no alternative, not just pressured into them by misguided morals.
Pottersville has more excitement and a superior economic infrastructure, but under the glamor many people live on the streets (and many of the ladies are hookers instead of homemakers). Bedford Falls only has a moderate manufacturing economy and no obvious places to find excitement, though the honesty and unity between the B&L and small business owners allows them to overcome most financial problems. Once the factory closes down Bedford Falls will suffer depression and unemployment. In the end, a place like Bedford Falls has a better chance of bouncing back from a bad economy because of the mutual cooperation between the banks and small businesses.
If you pay attention, that's actually exactly what happens: George suggests to a plastics magnate that he convert a closed tool-and-die factory and employ the locals. It's a minor throwaway line in the middle of a scene with much more important things going on, emotionally speaking, but it's there.
George makes it clear that he wants to leave Bedford Falls, go to college, and travel the world. All of his dreams are destroyed and he must commit suicide to regain hope and perspective. Potter was partially correct that George’s life has not resulted in personal happiness.
Pottersville being a gigantic Egopolis for Mister Potter is economically depressed to any obvious viewer. The fact that alcohol and hookers are freely available doesn't mean the town is Las Vegas, it just means it's people are trying to find some relief. Plenty of towns have died after going through something similar. Likewise, George is possessed of a beautiful family and numerous friends. George is mostly just wondering if he could have done more if he'd had different circumstances, a situation many people suffer from.
It Was His Sled: George Bailey gets sent to an Alternate Future where he was never born.
Jerkass Woobie: As a result of losing his son, Mr. Gower is a grumpy old man who is driven to drink and would have fatally poisoned a child if not for George's intervention; seeing his reaction to learning what he did and his fate in the alternate future is heartbreaking.
Moral Event Horizon: Mr. Potter is a hateful and greedy man throughout the whole movie, but what he does to George near the end is where he crossed the line and became immortalized as one of the most memorable and hateful villains in cinema.
Mr. Potter Why, George ... you're worth more dead than alive.
Narm Charm: George's unadultarated joy and relief when he realizes he's alive again. The endless shrieks of "Merry Christmas!!!" to every person and every building he meets should be Ham and Cheese at best, and Narm at worst. But in this movie, it's a cue for the Manly Tears.
Tear Jerker: The entire last act of the movie set on Christmas Eve, culminating in "I want to live again!".
Mr. Gower mourning his son, a victim of the Spanish flu pandemic, is also pretty hard to watch.
Values Dissonance: In Pottersville Mary is a single woman who works at the library. It is evidently supposed to be a horrible fate that she couldn't become George's wife and instead is an old maid. George's more personal horror that the love of his life never knew him and his children were never born though is still timeless.
In the movie's defense we can infer that, like the rest of Pottersville, that Mary leads a dreary and unhappy life when before she may not have had much, she had what she really wanted out of life. And what she wanted was to be a wife and mother is not wrong in itself.
Major Values Dissonance with Mr. Gower and young George. First, would George at that age be considered old enough to hold a paying job nowadays? Second, when Mr. Gower slaps George, drawing blood from his bad ear.... nowadays that would be a lawsuit, and probably jail time.
What Do You Mean, It's for Kids?: The whole movie is about a guy about to commit suicide. For one thing, the bar brawl in the Martini bar when George looks so depressed, and the whole alternate universe part, with other bar brawls where the Martini bar used to be; the attempted arrest of George and Clarence for trespassing at a still-dilapidated house; the hand-biting; the possible attempted rape of Mary; and it all ends with police attempting to shoot George by firing guns as he runs away. And this was under the Hays Production Code.
Not to mention all the sex jokes in the first act. Have fun explaining to a six-year-old that entire flowerbush scene.