I love Sins of a Solar Empire.
I loved it when it came out. It got even better with Entrenchment. But for me, Sins of a Solar Empire: Diplomacy helps take it to a new level. When combined, you get Sins of a Solar Empire: Trinity.
Don’t have Sins of a Solar Empire? Get it. Now. Stop reading this and go get it.
For every PC gamer who has loved games like Total Annihilation, Warcraft, Age of Empires or Homeworld, this is the game for you. It has incredible scale. It has truly unique factions. It has very easy straight forward gameplay yet it has real depth.
So what is a game like?  Here’s an example of a typical game…
Chapter 1: The Setup…
People who have Sins of a Solar Empire know this already but for those of you unfamiliar with it, what makes Sins particularly compelling is that it is a good single player game and a good multiplayer game. 
In multiplayer, people can save games and come back to them.  Someone gets disconnected? No problem, just get the game going again if you want with your auto-save. Or maybe you want to play an epic sized game with hundreds of planets that takes many weekends (ala classic games like Twilight Imperium). No problem.
But Sins of a Solar Empire: Trinity is a particularly good single player game as well. Ironically, the bulk of the work in the Diplomacy expansion pack has been on the AI.  The AI won’t just gang up on the human player at high difficulty levels anymore. They’re smarter. There are new difficulty levels. They’re just a lot more fun.

We also have a lot of new maps spread out in Diplomacy.  Having played the game for a long time now, we’ve gotten pretty good at figuring out which maps are the most fun to play.

The new difficulty levels make the game a lot more challenging. The newer levels give some resource advantages to the AI players but this has created some really interesting game options that were simply impossible before.

For instance, it’s really fun to have one AI player that is setup to be ridiculously powerful and then get some friends together to try to defeat it. That wasn’t possible before Diplomacy as its difficulty level topped out at “Unfair”.

The Game options have been really expanded. Besides the diplomatic victory condition, there’s also the much wanted “Faster” rates which helps make the game “move along” a lot faster for people who are looking for shorter games.
Chapter 2: The Collapse of Unity
…After 25 years of war, the Trader Emergency Coalition is being worn down. The arms race between the TEC, the alien invaders known as the Vasari and the vile fanatics known as the “Advent” has continued to escalate.
Unfortunately, 25 years of war has resulted in the fracturing within each group. In the star system Aeries, I am confronted with four lethal enemies…
Vaskorus Arkun is a splinter of the once unified Vasari Empire. Powerful, their technology is hundreds, perhaps thousands of years ahead of human technology. They have already conquered a planet from one of the TEC factions.
Hand of Illus is the local group of fanatics laying claim to this system. They too have taken one of the TEC planets.
 
Aluxian Resurgence.  Refugees of the two worlds that the invaders have taken have retreated to a final colony.  I give them little hope.
 
Lexmada. Lexmada is the one to truly fear. If she can be won over, there may be hope. Lexmada represents the corporate interests of the Trader Emergency Coalition.  If I had to bet on any of them, I would bet on Lexmada and their corporate CEO Imelarda Franco. She may be genetically human but I highly suspect that’s as far as it goes…
Chapter 3: Life on Vangelis
My home.
Vangelis has been colonized by humans for over a hundred years. During the noontide of the Trader era, Vangelis was one of the great sources of innovation and research. 
Until recently, this part of the old Trader space was untouched by the war. Now it is ground zero. We cannot survive through brute conquest. Instead, we will need to find the right balance between guns, butter and diplomacy.

The TDN Alteus is the pride and joy of our people. It represents the manufacturing might of our world and the hopes of our diplomats to back our envoys up with the threat of force.

This is the Neruda envoy cruiser.   My civilian researchers have researched the issue of building trust and gaining better relations a great deal. This research has culminated in the Neruda cruiser.  Now, I must find where to send it.

The new relationship screen lets me see where I stand with other factions. It has generally been easier to get better relations with humans for me.  The two TEC factions are already more favorable disposed (all relative – abysmal vs. hate) towards me.
The Aluxians are idiots. It’s Lexmada that I want to keep off my back.

Lexmada is relatively close so I’ll send my envoy there.
Meanwhile, the Vasari have already begun assaulting one of my asteroid colonies.


Luckily, the Alteus  is on hand.

At the same time, Lexmada is not…impressed with my diplomatic overtures. The last thing they see is an incoming missile.
So what can I do? What is damaging my relations? Luckily, in Diplomacy, I find see why:

Their fleet strength is just so much higher than mine that it’s bringing down everything else big time.  Their fleet is almost 4 times larger than mine.
However, I have been able to get a cease fire with the bungling Aluxians. But the Vasari press on.

Tragedy.
The loss of the Alteus is a huge blow.
But it comes at a great cost to the enemy.

We trade our flag ships.
Chapter 4: Diplomacy Offensive With negotiations stalled with Lexmada, their icy leader sends a military force to my asteroid colony of Prometheus. My last capital ship, the TDN Novick, is up against the wall there against a much larger foe.
There is hope:

The Rolaz has arrived to attempt to fast-build a starbase. If the Novick can hold out long enough for the starbase to be completed, we might have a chance.

The newly built TDN Vanifax has a novice crew but has been rushed into service in order to help hold the system.

Success!
The starbase, while not powerful right now, is enough to give me the edge.
NOW…
Let’s talk, Imelarda…

Now I can concentrate on the Vasari scum.
Got my cease fire with Lexmada.
 

And not a moment too soon. Luckily, the pirates have caused them to split their forces in two.

The battle wages above.  Now, I’m no match for the Vasari in this scenario. My ONLY chance is a diplomatic victory.
The Vasari have expanded and control much of the system now.
But I have other means…

In Diplomacy, I can now offer specific missions to the pirates. The more money I’m willing to spend, the stronger they get. Not just in numbers but in weapons too culminating with structure destroying weapons.
This will definitely make their life painful. 

Once the pirates soften them up a bit, I plan to come in and attack.
So what is my end goal here?

When a player is destroyed, the rate in which I accumulate points increases. Moreover, players with a 0 relationship bonus with me are probably dragging my score down (literally) so eliminating one of them will allow my diplomatic score to increase faster.
This is one of the really cool things about Sins of a Solar Empire: Trinity here is that you end up with so many different ways to play the game.
For instance, I could create a totally different game scenario based purely on who I set up as my opponents.  Let me show you:

So based on who I set up as my opponents, I can greatly increase or decrease the ease of getting a diplomatic victory.  Now, to be…ahem, honest, because I’m playing as TEC and half my opponents are TEC, I’ve effectively made it quite a bit easier to get a diplomatic victory since the different TEC factions are more likely to “get back together” than say my ability to get the Advent and Vasari to be friends with me. 
Again, this is one of the really cool and imo unique things about Sins of a Solar Empire.  Even more so than Galactic Civilizations, players can make each game its own truly epic campaign.  Now, admittedly, I wouldn’t have said that so much before Diplomacy because it was a lot harder to have any tangible influence over who liked whom.

On that same meme, in Diplomacy I can pay different players to go after one another.
Now that I’ve become friendly with Lexmada, I will ask her to attack the monstrous Vasari – at the same time as the pirates I recently bribed to go attack.
One of the things this sort of thing does, when done by an experience diplomat, is ensure that different factions don’t get too friendly.  In single player, this is pretty fun, in multiplayer, it’s really awesome.

Meanwhile, my envoy ships are in orbit of various worlds controlled by the Lexmada corporation. Not only do they help improve my relations with them but they generate a fairly sizeable chunk of money – about 1 additional credit per minute per system which can really add up.

And now to make my  move…

Taking on the Vasari and Advent with my new friends.
With the my two enemies gone, diplomatic victory is assured.

I’m getting close!

Diplomatic victory. The TEC reunite to hold the system!
Chapter 5: Aftermath Each game is different. In this scenario, I got some luck. Lexmada happened to be close by and was the most powerful (Lexmada was the random player I put in at the highest difficult, there was a 1/3 chance that it would come out as the same race as myself).
Consider this graph:

If instead of the TEC faction, Lexmada I had ended up with a Vasari or Advent enemy of that power, it would have been a lot lot tougher.
In addition, this was a relatively small system. Only 5 players, only a dozen colonizeable planets. Imagine dealing with say 3 star systems with 20 planets each how that might have gone.
That’s where the replay ability possibilities of Diplomacy come in. Players have a lot more tools at their disposal to deal with enemies and potential friends.