Nomad

Nomad is one of the world's great, but nearly forgotten, space exploration games. While it had a somewhat weak storyline that really only comes into play early in the game, it makes up for it by allowing the flexibility to manipulate the story yourself, rather than being tied to a particular path and order of completing tasks.
Game play offers a number of choices, requiring you to make decisions about your own allegiances. Of the several races in the galaxy, few get along well with each other, some are outright warlike, and even the two energy based races can't agree on much.

As might be assumed, some races will reward you for various missions against others, including espionage, taking out freighters, and eliminating warships. On the other hand, most people don't like being attacked and aggression will typically close down relations pretty well, though some individuals are more forgiving than others. Each race typically has one technology where they really shine, so keeping relations good to be able to build up your arsenal can be critical.
Despite the battle aspect, it is the smallest part of the game and a truly dedicated player can achieve a victory without ever firing a weapon. Battle lacks most of the depth of better space simulated combat games such as Frontier First Encounters, with missiles being the only offensive weapon. Combat eventually becomes very easy with 99% accurate missiles that will take down all but the two most powerful ships in a single shot.
Trading and exploration is where Nomad really shines. There are around 300 different items, most available for trade, and even the most stupid looking can be essential to winning. Some items must be found on abandoned worlds with Arch Bots, while others are stolen from inhabited planets with Spy Bots. Farm Bots can grow food to trade, while Ranch Bots round up the meat. Even the most unforgiving worlds have their uses with Gas Bots and Ore Bots. Of course MOST (not all) of this junk is fairly useless alone, but the right guy will always give you some of his junk for a bunch of yours...of course I should shut up now before I get spoily.
Ultimately, there are at least 3 separate ways to win, each with an entirely different path to victory. This stands in stark contrast to the typical "multiple ending" game, where you must still follow the same basic path every time. It's worth it to play until you win once each way, the ending is lame, but the journey is the reward.