Quoted from jonesjb:

I FINALLY had an opportunity to play a Congo, and now I'm a position to comment. Congo is a great game, it's fun, there's some great flow, nice ramps, and some unique action at the top of the playfield. I think the art is quite nice, reminiscent of an Indiana Jones adventure. However, I could see myself tiring of it sooner than a Shadow, so I think it works in a larger collection. It's definitely fun, the kind of game you could come back to, and is more accessible for non pinball players. I'm not a fan of the lower playfield... It seems random, but the volcano is so cool!
If I had to pick, I'd choose Shadow however. Shadow is deeper, has amazing flow, more of a challenge, clever modes, better video mode, booming sound, and offers many ways to approach the game for high scores and wizard mode. There is lots do do outside of wizard mode and will definitely last longer in a home collection. It also has some cool toys, like the Sanctum, diverters, and playfield. My pick goes to Shadow.