How does one make a sequel to a basically perfect game? 2007's physics-platformer-in-a-weird-science-facility Portal is a lodestar piece of game design from top to bottom. It's one of my favourite games, and I went into 2011's Portal 2 with many a reservation. But it's very good! And there are so many things I love about Portal 2 that it's quite hard to pick just one thing to write about.
I could do "the joy of Portal 2's retro science", where you fall through the floor into the old school Aperture Science labs and see the 60s-ish version of all the big buttons and testing chambers you were put through in the first Portal. I could do "the joy of the corrupted personality cores in Portal 2", a group of corrupted AI spheres including Rick The Adventure Sphere, which is largely just Nolan North making up his own action theme song. I could even do "the joy of potatoes in Portal 2". And then I realised that most of the things I like about Portal 2 also intersect with Stephen Merchant's character Wheatley, a weird little guy (in the most pejorative sense).