I played this game's immediate predecessor, Weird Worlds, extensively, and made the "Odd Adventures" mod that racked up a little notoriety near the end of that game's shelf life with Shrapnel Games. As a result, I'd dare say that I have more experience with the Infinite Space series than anyone who hasn't actually worked on the games or made a large-scale modification of their own (Hi, sgqwonkian!)
I say that to say this: if you liked Weird Worlds, you will probably like "Sea of Stars", but the game's future will depend greatly on how much Digital Eel has put into this game's engine. If the modding options really are "all that and the kitchen sink", SoS should be able to have a good run... if not, it's little more than an incremental upgrade, with a few jarring changes from the comfortable SAIS-derived interface that will disconcert both newbies and veterans.
The most obvious change is that the game is now 3D. Unfortunately SoS seems to get all the worst aspects of this change: the ship models are not especially detailed, arguably being a downgrade from the 2D graphics in Weird Worlds. The combat is a 2.5D compromise, which retains a lot of the simplicity of the original game, but sacrifices perhaps the game's best chance of distinguishing itself from its predecessors. The star map is fully 3D, and this is every bit as disorienting as you would expect. It's pretty, but that's about all I can say for it; as the actual gameplay doesn't seem to differ in any way from what's provided by a 2D starmap, it seems like a change made for the sake of change. Various fans have suggested making the starmap a 2.5D map, with all the systems shown on a flat plane, and I can't say that I disagree with the idea; right now attempting to navigate the purple void is downright painful, compared to the easy play that was present in the previous two games. That said, the planets and stars look spectacular on a full screen, and the ability to freely rotate gives the player a lot of interesting views that they would have missed in the previous games.
The combat system is very similar to the one in WW, and retains many of its flaws, while adding a couple more. I'll start by mentioning the biggest improvement: you can now set exact paths for your ships to follow. Previously, your ship would go in a straight line to the coordinate you directed it at; now you can do something a little more elaborate, without having to keep your mouse over the ship.
As a tradeoff, though, It is now painfully difficult to control fighters in combat; ships don't seem to stay selected the way they used to. You have to drag in the direction you want the ship to go, and when you're in a fighter, that is simply not convenient... they keep slipping out from under the mouse. The way the game is set up discourages giving fighters the precise orders that made them so helpful in previous games in the series.
One interesting change is how the ships are deployed; in the previous game, you would pre-set a "formation" that your ships would appear in at the start of the battle. Now, you can dynamically deploy your ships anywhere on the map at the start of the battle, which gives you a few new tactical options that weren't available before. You also have the option of which ships to put into the fray; if you don't want to risk your weaker vessels in a hard fight, or your fleet on a first contact mission, you don't have to. Retreating is still cheap and easy, but your ships are now delayed for a second or two while they go into light speed, which gives your enemies a little time to hurt you before you run.
All in all, though, the combat is not a big improvement on SAIS or WW. It retains the same problem of being largely pre-determined after the initial ship deployment. I had mentioned in a post on the old WW mod forum that WW (and obviously, any successors) might be better served by having a more arcadey combat engine, and this is still the case. There isn't much in the way of tactics or ship maneuvering; most of fighting is just point your ship and shoot. For something that is such an important part of the game, that's less than desirable. Nowadays FTL is the definitive combat experience in space Rogue-likes, and SoS doesn't match up. The combat mechanics were decent back when SAIS first came out in the early 2000s, and tolerable in Weird Worlds in 2007, but it's looking very dated in 2014.
There are a few enhancements to the general game. Hope's Haven Station now handles transactions in credits, which has potential to make things very interesting for modders if the purchasing is handled as flexibly as it ought to be. The combat simulator now allows you to customize your ships, and includes a "tech level" slider for opposing fleets. This alludes to the possibility of having enemies that become more advanced and invent new ship classes during play, which is obviously exciting for modders. You can buy new ships from Haven Station with your earnings, which makes losing ships less painful and allows you to get better use of your profits from exploration.
There are also a few curious omissions in the current game. Firstly, there doesn't seem to be any option for customizing your mission's length. Secondly, the flavor text that existed at the beginning and ending of WW is entirely missing. You no longer return to Hope in glory to retire as the Fleet's new admiral, or get shaken down by thugs and left to rot as a funny-spore farmer; instead, you just get a short blurb that notes you retired/died in combat/got eaten by a space whale/whatever, and your score. I suppose dedicated players will write their own narratives, but at a first glance this definitely seems to take away from the immersion in the game. Finally, the combat simulator lacks the friend/foe options that existed in previous versions of the game, which makes it a little harder for someone who wants to create a multi-side grand battle. SoS is still in development, though, so perhaps these problems will be resolved in later versions of the game.
The bottom line... do I recommend this? Like I said before, a lot of what SoS does is based on the previous games in the series. If this was 2007, I could say that it was the best thing still going, but with new competition like FTL, other new Rogue-likes, and a growing interest in procedural generation, I'm not sure that SoS (or WW, for that matter) is really at the head of the class in any particular area.
That said, though, SoS has the potential to be everything that WW was, and then some. Considering that WW retailed for something like $15-20, and this game's price seems to be capped at $10, that's something that you need to think about. The Infinite Space games have always been at their best when modded, so if the interface's rough edges are smoothed out, and the developers' promises of extensive modification options (presumably greater than WW's) hold true, SoS should turn out to be well worth the expenditure. I'm giving it a qualified recommendation. Here's hoping that Digital Eel can close the deal and make SoS into an unqualified success.