MC Kids is superficially a mix of elements from Super Mario 2 and 3, but it's really more of a puzzle-platformer than any Mario game ever was. Sure, you got the map design cribbed from Mario 3, Luigi's squat-jump for extra vertical hops and the samey-feeling lifting and throwing of blocks from Mario 2, and etc. But fundamentally each level is more about making non-obvious jumps and exploring vertically to find hidden cards than it is about going from one end to the other dodging pits and enemies. Levels actually showcase some unique and inventive stuff that is more like something you'd see in a 2000s "throwback" indie retro platformer, like whole-stage gravity reversal that forces you to retread your steps going underneath platforms to get the various cards and goodies that initially seem out of reach.
All that said, it's good, but not fantastic. There's some running mistakes in the level design that you keep seeing over and over, the biggest being trial-and-error dives into pits where you basically have to die at least once to see where you were supposed to land. Enemies aren't a huge threat, but they do appear (along with traps) very suddenly as the screen scrolls, often another case of taking an unavoidable hit at least once to memorize where they are. The graphics are also on the spartan side, even for the NES.
Most of the level design irritants are mitigated by the fact that extra lives are very plentiful, however. When you find a rich vein, you're free to replay that same level over and over to harvest them.
Though I wouldn't say it's one of the absolute best 8-bit platformers, it's a very solid one that does some things that others weren't doing at the time, and I think it definitely merits a look for genre fans. It's definitely better than any licensed McDonalds game in this era had a right to be, and I think the miscues in level design are more on Virgin being out of their element making a console platformer (they were biggest into PC RPG/adventure) rather than a lack of effort.