Superman is such a mixed bag. It has a few cool ideas, and some really good shots, but it's also hampered by several things.
First, I should note that the art looks great. Playfield art and backglass both give the comic book vibe from the era. George Opperman may have been Atari's greatest asset. Cabinet art is pretty tame comparatively, in that limited color stencil style favored at the time.
The playfield is well lit, and given the bright colors I think it is pretty easy to keep track of the ball.
The play itself is mixed, so let's hit the good parts first. I'd consider the main goal to be spelling SUPERMAN. Nothing spots letters, so you have to make all the shots, and they require you to play the entire table, so I think that's well implemented. There is a drop-target bank in the center; completing the drops advances the kick-out hole's award, so you can choose to take the center-shooting risk and try to light that for more value. There's also a roving lit drop target (reminds me of Tri Zone, another 1979 game) on the bank which can be hit for additional points. The game has two spinners, either of which can be lit, and they can be a lot of fun. I also really like the lower-pop on the left-hand side. It gets a lot of play in games, and introduces a lot of action in an otherwise slow table.
So, the bad parts. Well, as my last sentence in the good section demonstrates, this game is slow. All the Atari games are widebodies, and this suffers as you'd expect. Big outlane sections, lots of (slow) side to side action, and sometimes significant time waiting for the ball to actually interact with something. The Fortress of Solitude shot is long (better have strong flippers to make it), and it takes up a ton of space. Outside of hitting the spinner, all it does is have an elaborate path back to the top of the playfield. It is sort of neat to see, but it requires such a strong shot that you'll just wish the game had an orbit instead. Luthor's Lair is easier to make (the ball has less routing to deal with) but it also is pretty lackluster outside of the spinner.
Sounds are fun, but no background music is a disappointment (not surprising for the time, but knowing that the designers wanted to add it in and Atari said no just makes it sting knowing it could have been more immersive).
Overall, Superman is a decent pin. Steve Ritchie's design, while not consisting of the flow he is now known for, does offer a number of shots, and the rules incentivize taking those shots. But even steep the game doesn't play particularly fast, and you MUST have good flippers in order to reach the top of the playfield. But if you see one in decent shape, this can be entertaining and challenging.