I've been reading some topics in the Atari 7800 forum and I've found great arguments about why Atari 7800 fans don't like Fight Night. I came to the conclusion that I needed to share my opinion with the community: I like the game, even if it gets bad ratings for good reasons...
First of all, I don't think this boxing game is underrated: it is bad, but not unplayable. The first time I played it, I was so upset: the characters looked great, but the controls were horrible and the gameplay was confusing and frustrating. My second experience with the game was better: I knew how to make the "super punch" and got used to the controls. But once I discovered how to survived longer and won the Main Event, I started to appreciate Fight Night. I'm not saying that it's the best of its kind(the animation is choppy and the controls are terrible and somewhat unresponsive), but I find it quite enjoyable. It has a neat tournament mode, as well as sparring matches. I've played the XE version of this game but not the Commodore 64 port (which looks superior in many ways, but I haven't tried it yet, so it wouldn't be fair if I compared them). The boxer construction set is a pretty interesting feature, but I didn't like this port because I thought it was too slow. I have a theory that could explain why they didn't include it in the Atari 7800 version: the games in the Tramiel's era (or, at least, in 1987/88) were made with tight budgets and the XEGS was considered the "premium" game system by Atari at the time (situation that probably doomed the 7800 port of Karateka), so the programmers tried to compensate the lack of the construction set by creating six custom characters using parts and colors of the original characters and making them "new" selectable characters. Anyway, even with the quality of the game, I still think it's fun.
So, in my opinion, Fight Night could get a 5/10.