Wonder Boy: The Dragon's Trap (mentioned around the middle) is IMHO a fantastic example on how to modernize an old game.
Not only they reused the original source code, but you can switch between the original and remastered graphics and music at any time, and even separately in any combination. It also allows you to generate a passcode so you can use your "save" with the original game, on top of being able to accept original passcodes as well.
It was a true work of love; the main coder, Omar Cornut, wrote one of the major SMS emulators and this was his favorite game. I suppose that talent like that is hard to find for every single game, though...
I had some kind of Pong paddles that connected to the TV in the early 80s, thought I don't remember when it was bought. It had 4 or 5 games on it including one-player "squash" against a wall. It had no brand but it was a couple of rectangular paddles which connected to the TV via RF. Like an early version of those TV-only game devices with retro games.
Along the same time I had that brown Mattel Soccer handheld. My first console and portabke gaming systems
I still have both but they aren't working, sadly. Still cool gadgets to have on the shelf.