The Great Giana Sisters is a pretty straightforward Super Mario Bros. clone. So straightforward, in fact, that publisher Rainbow Arts was forced to remove it from shelves under pressure from Nintendo's legal department, leaving those children that didn't snatch it up quickly enough to hate their parents for buying them a stupid computer instead of a Nintendo.
I think that if 12 year old, Commodore 64 owning me had owned The Great Giana Sisters, he would have thought it to be an adequate replacement for Super Mario Bros. All the children at school from Nintendo owning families still would have thought he was a freak and excluded him from their video game conversations, causing him to grow up a social outcast who makes fun of video games (even ones he kind of likes, because that's more entertaining) every day, but at least he would have had something to do when he got home from school.
The Great Giana Sisters goes so far as to copy not only the game play basics but in some cases level maps and the lame boss fights from Super Mario Bros. The giant lobster thing at the end of every third or fourth level will just leave if you jump over him. Also worth noting, taking a hit while powered up does not simply revert you to your non powered form, it kills you. On the upside, you can still skip most of the underground levels by running through the status part of the screen.
It's nice that someone thought of all those poor Nintendoless children out there and tried to help them. Too bad Nintendo had to go a ruin it all by going legal on Rainbow Arts, though not at all surprising given their monopolistic tendencies at the time. I'm surprised they didn't try to sue Atari and Sega, saying that their video game consoles were nothing but copies of the NES. Or sue Commodore and Apple, claiming that the disk drives they used were copies of the Famicom Disk System. Or sue my parents for not buying me a Nintendo Entertainment System.