fvwm (and fvwm95) were attempts to make "friendly" desktops that looked a little like what most MS users were using at the time. They're alright, but for the most part they've been surpassed as relics. There are plenty of people that still develop them, and they make fine desktops for systems that don't want to have to meet some of the higher requirements, but if you're comparing the two, Gnome and fvwm are two different beasts.
Gnome...way back when...was a lot like fvwm, as was KDE. From there, the resemlbance ends. Gnome and KDE have a lot of other stuff added on. In fact, Gnome and KDE are properly called desktops, meaning they are composed of much more than just the stuff included in the "window managers" like fvwm. To be honest, this stuff is confusing, and it often blurs the lines, so there's no easy answer.
Simply put, fvwm(95) is the low resource, pretty desktop. There are "better" ones, but it's up to your system resources and preferences to decide which is best for you.