Machine Wars (the 1997 original) was such a fascinating little capsule. Entirely new lineup, name reuses in a still continuity-oriented era that more strongly called for fiction with explanations for how x character is now in y body or z state of being alive (as opposed to decades hence, when we're just "oh, they needed to renew that"). Plus, of course, there were bios to give us something to work with.
And the departures from what was established were so damn interesting. A faceplate-less Optimus Prime, an immense Starscream and entirely different-looking Seekers, Megs with a clone, missile tank Soundwave, and an unexpected lineup of characters in Prowl, Sandstorm, Hubcap, and more. All in the middle of Beast Wars, a wholly distinct story with its own fully developed cast. This was fun to brainstorm story concepts for, whether as a bridge between G1-2 and BW, a diversion within BW (hence the name), or its own universe.
Funny enough I think the Botcon comic for that year is one of the better ones. It manages to craft a newish setting and story that's fun to find out more about. This and the G2 Redux one were great for that.
The year's slate of exclusives was an odd one, despite the intriguing blend of Machine Wars and Vehicons.