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.
Moment Of Awesome: A contestant plays Contact for £50K - essentially a "steady hands" game where you have to guide a ring along a long metal rod without it touching - and nails it on his first try, giving him 5 lives and both Lifelines available for the £100K game.
Same for its other appearance as the very last game in Series 1, whose contestant had three lives for £20k. Goes down to the last life after two poor attempts. Out of nowhere, he somehow manages to clear all three metres and win.
Series 3 add a new moment to the list: a contestant has three lives and a Trial Run to play Hit Rate for £50k (a game in which the player has to hit five pads on a curved table within half a second). He uses his Trial Run and gets a time of 0.588. He commits, to the shock of pretty much everyone in the studio. His first two attempts get him down to a time of 0.513. Cue the entire audience behind him cheering him on, as his very last life gets him a time of 0.494, winning the game (and £50,000) by just six thousandths of a second.
On a July 2012 Celebrity Edition, British runner Mo Farah managed to become the first person to ever beat the final round (a harder version of Barrier in this case) and win the £250,000 grand prize (for charity, of course), with only 6 lives remaining. But then he took things a step further and won Britain's first gold medal in the Men's 10,000m run at the Olympic Games in London. If you can beat The Cube, anything's possible!
Surprise Difficulty: Doing simple-looking stunts inside a glass box is much harder than it sounds.
It's Easy, so It Sucks: Counter to the above, some people think the show's premise is stupid, particularly for trying to give the impression that something easy is somehow more difficult when you're in a glass box with coloured lighting. Radio host Chris Moyles has probably led the charge on this:
"I'm watching a man count inside a box." "It's just counting! But it's counting, IN THE CUUUUUUUBE!"
That One Level: This show is chock full of them. Conceivably any game can get the TOL treatment if a contestant goes in with 8 lives and watches them dwindle down to nothing as the same task mocks them. Generally the truly wicked games fall into one of two categories:
Steady Hand games:Construct, Pinpoint, Composure, Tremor, Structure et al. These games are frequently played towards the tail end of a player's campaign, and all of them require the player to either negotiate an object along a track while not touching the sides or building something out of small pieces against a clock and/or without it falling apart.
Physics skill games:Pendulum, Cylinder, Descent, Circumference, Arc et al. These are the games that often look deceptively simple, but when a player actually tries it they fall into the pattern of missing on the first try, then overcorrecting on the second, then getting frustrated, then burning their Simplify, then getting down to one life, then barely escaping with a win on their last try.
Unwinnable by Design: Only a handful of non-celebrity players have even gotten to the £100,000 level; none of them have attempted the £250,000 game, mainly because they risk losing all of their winnings if they fail. A recent S6 contestant refused to play the final game - Descent, the only game he lost more than one life on - despite having six lives and his Simplify. It didn't help that his wife in the audience made an inappropriate joke about threatening a divorce if he tried it.
What an Idiot: Zoe, who used eight of her nine lives on her first game Time Split (stop a timer on exactly 5.0 seconds). She proceeded to use Simplify after her fifth failure (either undershooting or overshooting the mark by mere tenths of a second), which changed the timer to count in increments of .2 seconds. After finally winning that, she proceeded to fail on Stabilise. The fact she had a bizarre fascination with wigs didn't help matters, either.
Series 6 Episode 2: Nicky and her boyfriend Mark both demonstrated a complete lack of understanding of basic (freshman-level) rotational kinematics playing Pendulum for £2,000. Mark told her to throw the ball hard. She did, and it went way over the target ball. Repeat for a total of eight lives lost and a Simplify, all while she and Mark kept mulling over whether to start the swing higher or lower, and Mark kept telling her to throw it hard, when anyone who's taken Physics 101 (and any particularly observant child who's swung around a ball tied to a string, or rolled a marble inside a bowl) should know that it's the rotational velocity that matters.