This is probably not the kind of suggestion you're looking for, but a quick fix would be some kind of AI rule that makes computer players surrender when they're quite obviously doomed (i.e. decimated fleet, no resources, down to a handful of underdeveloped planets, and your massive fleet jumping from system to system annhiliating scout ships and constructors).  I've not played multiplayer extensively, but I would think most human players would surrener at this point.  I certainly would.

Another, slightly more complex fix would be to institute some kind of capital planet rule for victory conditions, though with the ability to move one's capital that could get a touch hokey.  I'm not even positive on what happens if a capital is destroyed... is it automatically relocated or is the player capital-less until they choose a planet and spend the neccesary resources?  The trouble with the "key world" is that it can be located anywhere in your empire... and if a rim-world capital falls, it's still compeltely feasible to have a burgeoning empire intact behind it.  Hence, I suppose, the strategic relocation of one's capital.  I'm clearly undecided on this.

It seems to me there was a game... maybe one of the Civs or even Alpha Centauri... in which a mostly-defeated opponent could be diplomatically persuaded to become a "vassal-state" of the conquering player.  I don't recall exactly how this worked but I believe heavy resource "taxes" were involved, as well as the expected protectorship of the conquering nation.  Now that I'm talking about it, I believe it's actually Civ IV that has this feature, though I dont' think I ever got it to work properly.  Some allusions have been made that diplomatic options are to be elaborated upon in at least one of the upcoming micro-expansions... perhaps we can hope for something of this nature?  I for one enjoy the concept of having Vasari slaves to mine my metal and crystal =P

Having different victory conditions could help this too. (ie. 75% of all occupiable gravity wells, wonder victories, timer victory, research victory, as mentioned capital victory).

Yeah, I'll agree that the pleasure of the game tends to level off in the very late stages. You have complete ownership of two of the three star systems, and three quarters of third, and you 1500 point fleet is two hops away from the last planet.. but they insist on sending a level 1 capship with 7 frigates out to attack you.

I kind of feel it's like my fleet commanders have set little speeches for the newly conquered " Um, yeah, so welcome to the empire and all that, we'll be building a few things in orbit, and doing a few upgrades to the infrastructure... it's all in this little pamphlet "

Let's be honest. When you eventually break through the last really challenging encounter, there is nothing more to focus on. Should there be? Not really. After all, this game is about defeating the enemy, NOT building a fancy lookin' orbital sim(n) city.

I think tweaking the AI behavior in face of defeat could help. Make the AIs auto-surrender when you really are nowhere near defeatable anymore.

Sins isn't the first game to suffer from this type of problem.  Perhaps they should include some sort of an option to have the computer compare the size of your fleet and economy to the other races' and then declare victory once the game has been clearly decided.

Note that if you're interested in playing more interesting games, I highly recommend that you consider playing the game in online multiplayer against real human opponents.  Not only will you be able to chat with teammates and the other players (and to try to coordinate teamwork), but ou'll find that it's more challenging and that the prospect of actually losing makes the games much more intense and satisfying.  Also, people tend to quit or surrender once the outcome of a game has been decided.

My friend... Now you know my addiction.  Why bother sending fleets from world to world, when you can just send an army of scouts to find the enemy worlds and mass novalith them?  (IMPORTANT NOTICE: Novaliths are restricted to planet nuking planets in the same solar system) I am considering mass novalithing (Fun term) on one of my saves. 

With novaliths your fleets can guard the chokepoints, and the novaliths can do the planet nuking.

Yes, the game definitely begins to drag in the endgame after you've slapped down the opposing fleet. But I find the problem is that most times, you don't even really get to slap it down, since the AI will retreat their fleet when it looks like they're losing the tide of battle. This might be realistic, but it's also frustrating as you watch the enemy slip away to subspace when you really want to pound them down. Perhaps an expansion could introduce a cruiser that mounts a small phase jump inhibitor? It seems like a no brainer to me.

I also wish there was some sort of victory condition that lets you win the game if the original enemy capital planet is captured. This would greatly cut down on the mop up stage, as you wouldn't have to chase down the enemy as it repositions its home after every defeat. Having to slowly grind down the enemy and capture every single planet along the way is what really drags down the endgame and makes it tedious.

Maybe there could be something along the lines of what End War has where the losing side has a 'last ditch' tactic they could use once to try and turn the tide or at least become a threat once more? What exactly though I don't know. For now I just quit the game when the enemy has nothing left to threaten me.

Regarding the fleets retreating constantly, I do find that annoying at times too but it is also something human players would do. I think it would be better if it varied though. There should be fleet admirals that would risk a battle and not retreat at the first sign of a slightly larger fleet arriving.

yeah I find that annoying to, not so bad on the mdeium maps but but on the large and hue mmaps its a right cow even throwing your entire fleet into cleaning takes a while

why on earth the surrender feature doesnt work muc i dont know ,,, ive only seen it used twice by the ai, its too damned stubborn