Uh i really liked STar Wars Rebellion
Whether it is a 4X is disputable. You need only to expand by conquest. Explore is only really needed to find enemy colonies on the rim and even that not always. There are only two sides. No diplomacy. Very basic research. War, war, war, this is the only developed part. And some character management but that is hardly a 4X trait.
However, let's consider for a moment that it is a 4X.
It is fun for a short time but ultimately very mediocre.
- AI is bad, worse than average in a 4X.
- Easy, see above.
- Game, despite relatively simple mechanics, has bad micromanagement issues with both productions and missions.
- Tactical battles are badly done despite being a selling point for the game at the time iirc. Also not needed to win and there is auto resolve.
- Unique characters' role is underdeveloped. Most episodes 4-6 characters are in game with some nice mechanics like growing ranks in force and random chance someone non-canon might be Jedi. Fun! And useless. I suppose one could LARP.
- Many different special missions to perform, except not really needed and very annoying to manage in quantities.
- Mechanic of strategic space warfare are too simple, combined with bad ai, it is very easy.
a) Build and concentrate some production facilities
b) Build a fleet. Usually not needed to fight big battles but for the next point:
c) Find a sector with enemy controlled planets but some of your loyalty. Enemy fleets will be very small or somewhere else (AI, remember). Incite a rebellion on a planet. Once 1 or 2 planets have won their rebellion, all others in sector are doing it on their own. Winning a rebellion on a planet is a big swing in support in whole sector. Voila, sector is yours. After ~2 core sectors taken the war is effectively over. No need to fight big space battles at all. It's not even a real exploit but a game mechanic that makes sense. The only issue is that you can't wait too long to do it. One of the few things AI can do is increasing the loyalty on his planets to 100% (possibly cheating? can't remember).
You could use some self-imposed challenges but that can be said about tons of mediocre games and not an answer.
Boring after one or two games, Maybe 3 or 4 if you are a huge Star Wars fan. The first (very) few games are fun but from a 4X, you expect more longevity than that.