In terms of pixels, nothing has changed. Pixels are still pixels, the average screen just has a bit more of em. Well, okay, maybe there's been two changes to pixels since the 70's:
1. Tube screens to flat screens. Tube screens tend to do a lot of things to pixels, especially when the cheaper models get old. All of these blooming effects, aberrations, etc, were influential to how pixels behaved.
2. High DPI screens. Recently, we've started to see the disappearance of the pixel as a visible unit. In a few years, there will be screens of a high enough DPI that working at the pixel level becomes essentially useless.
So yeah, not a lot happened to pixels over the years, sorry to say.
How did games change? Well, a lot, and not at all. Each year new techniques are discovered and games get slightly more powerful visually. This is a collection of thousands and thousands of innovations though, it's hard to compare on to the other. The best way is to compare screenshots, hence me giving you screenshots that compare old vs new. If that's not what you need, you need to be a little more clear.