This was true even into the Game Boy Advance era (so the early 2000s). Have a look at how the box art for Mario Kart: Super Circuit compares to the actual graphics.
Admittedly, there was a general assumption that the box art (or even trailers) need not reflect the gameplay at all (and it was still a time when sufficiently high resolution graphics would be assumed to not be part of the actual game since it would be impossible), so there wasn't exactly much deception going on. But it could certainly still be disappointing if you're a child who doesn't quite know that. It's worth mentioning as well that the back of the box usually had some screengrabs to give an idea.
I remember those boxes. For the most part the VCS/2600 was so popular that most everyone knew what was what and that the box art was just that: art. There were few exceptions such as the infamous E.T. the Extra-Terrestrial. Pac-man was also a bad looking port, but playable and a commercial success.
Admittedly, there was a general assumption that the box art (or even trailers) need not reflect the gameplay at all (and it was still a time when sufficiently high resolution graphics would be assumed to not be part of the actual game since it would be impossible), so there wasn't exactly much deception going on. But it could certainly still be disappointing if you're a child who doesn't quite know that. It's worth mentioning as well that the back of the box usually had some screengrabs to give an idea.