WhipperSnapper
Lifer
In a 5v5 you would have a chance to win if your 4 allies could carry you. One thing I like about team games is that you have a little less pressure. You personally could get beaten down and your team could still pull out a win, and you might still be able to contribute to your team. (What if one of the opposing players also gets crushed, making it essentially 4v4?) Large team games introduce new strategic elements and alternate ways to contribute.
Entrenchment introduces another tech tree and starbases. It solves the problem of fighting on one front and being unable to defend on the other. You can build powerful starbases with all sorts of abilities, such as the ability to prevent loss of a planet if it gets bombed out. (The attacker has to destroy the starbase first.) Some of the defensive structures also gain extra abilities. The Vasari starbase can move around the gravity well and chase down enemy ships. You can also use Vasari starbases on offense. Entrenchment also adds Quickstart. With Quickstart you start with all of your resource extractors and your capital ship factory built, max terran population, and two scouts. (It shaves about 5 boring minutes off the game, but it could be argued that it screws over the Vasari.)
Diplomacy includes everything Entrenchment has and adds a diplomatic relations system. It also adds a Faster game speed level and two new AI difficulty levels--Cruel (3x eco) and Vicious (4x eco). The pirates are no longer a joke and can be very dangerous (if not overpowered). You can also offer other players specific missions. It introduces a new "relationship" system and you can build diplomatic envoy ships to improve your relationship with other allies, eventually allowing you to enter into game-changing "pacts", such as 20% more laser damage.
It depends on what you're looking for. I'll give two answers:
Single Player only: Entrenchment essentially decreases the difficulty level of the game because the AI has no idea how to deal with starbases. You can build starbases, upgrade them, add some fortifications and perhaps keep a small defense fleet around and the AI will just suicide on them. Also, the AI will waste its own money building starbases it won't defend. If you're an experienced or skilled player you can easily exploit all of this.
Diplomacy (which requires having Entrenchment) might be an excellent addition for single player. However, you might want to play with pirates off.
Multiplayer against human opponents: Entrenchment was an awesome addition to the game and added to the game's strategic considerations. It's much better with Entrenchment. However, there aren't too many people playing it online now since most people who had Entrenchment bought Diplomacy.
Diplomacy doesn't really add much to the online multiplayer game other than the possibility of entering into pacts with an ally and having to research the ability to "feed" credits and resources to allies. In fact many Diplomacy games feel just like Entrenchment games. The reason to purchase Diplomacy is because that's where the pro community of experienced play 4v4s and 5v5s resides.
Now--the really big question is, "If I want to play Sins in online multiplayer should I drop $20 on the two expansions?"
Probably not. Unfortunately, Sins has just always had low online player counts for various reasons. Also, Starcraft 2 consumed about 40-50% of the player base. This means that for your $20 will buy you the privilege of being able to log onto the Diplomacy game lobby and wait (and wait) for a game to fill. Also, the people who play the 4v4s and 5v5s are mostly highly experienced pros and you won't stand a chance against them, at least not without getting about 100 games against human opponents under your belt.
However, the biggest issue right now is just the online player counts. As I write this (8:15 pm U.S. EST), there are 23 people on the Regular/Entrenchment server and 26 people on the Diplomacy server, including people who are currently in games. This is during North American prime time. Also, more than half of those people only play with their friends against AI, so it's become very difficult to actually finda pvp game that's anything other than 1v1 or 2v2. 4v4s and 5v5s still happen on Diplomacy, but mostly on the weekends.
I hope that people reading this will buy the expansions because this game desperately needs more people online, and it deserves to have more people online. However, you have to decide whether that's worth $20 to you. Personally, even if I liked regular Sins, knowing what I know about the current player counts, I wouldn't spend $20 or even $10 (for Entrenchment) on it.
I suggest starting out online in regular Sins to see if you like it. Then you'll be better able to decide whether or not you want the expansions.
