Generations was a childhood game for me. Everyone who played it had difficulties progressing. It was only after I began revisiting the game across the years that grasped how intricate it is.
Every mission feels somewhat like an episode of the show, with each environment having its own story to explore. Some are mysteries, some are battles, some are puzzles, and most of them have all of these aspects combined. You can approach missions in a variety of ways, find secrets that make the mission extremely easy (or hard, yet rewarding), or that expand the Star Trek universe, and even the movie it's based on itself.
Every mission has a hidden timer that pressures you forward. You have one nemesis, Dr. Soran, who is constantly creating new challenges for you to overcome and hiring new goons to protect him. The game has an almost full cast of voiced characters with actors from the show. In my version, it was even dubbed with the official voice actors of my country. And characters seem to have reasonable and meaningful observations about their environment, or dialogues with NPCs.
A first playthrough will not reveal how branching the game actually is. It is possible to fail in your missions, up to two times, which will influence the story in such a way that you might get sent to a completely different planet next, with a completely new mission that you wouldn't have found otherwise.
Likewise, ground missions may be skipped entirely if you successfully identify Soran's location in space, guarded by a fleet of alien ships, and win in a decent gameplay of space combat against them. It is actually possible to beat the game without making a single ground mission after the first by just winning space combats--although that becomes extremely difficult after a point.
Space battles, win or lose, also affect the next mission, making it so that you can always explore more and more missions that you didn't even know existed.
This game is a work of love, worthy of eternalization.