Differences in gameplay between the different versions.

Well vanilla is the base game. Entrenchment adds in starbases, mines and anti-structure cruisers. Diplomacy adds in diplomatic options and more levels of AI on top of Entrenchment.

Get Trinity (it contains all three) for the best buck and/or wait for Rebellion which is coming soon and will add more contact. You get a discount on Rebellion later on if you buy Trinity no. About $10 US.

Right, thanks for the reply! 

Do those changes drastically change the way a game plays out? Esp. interms of pacing and overall strategy. Or does it just add some new cool features but nothing game altering.

I guess my motivation for asking is finding out if it makes sense to get Trinity AND Rebillion so that I could play the different game styles (Say, more turtling with Entrenchemnt vs. more in your face full out invasions with vanilla). 

One of each.

Entrenchment really changed the overall pacing and strategy with its starbases.  It opened up a whole wealth of new approaches and tactics.  Definitely a superb improvement to the game.  Aside from playing multiplayer with friends who only have the base game, I've never looked back from here.

Diplomacy definitely is the latter; it added some cool new features that only altered the game subtly.  It's definitely the weaker of the two expansions, but not bad in any way.  In that sense, there's really no reason to go back to Entrenchment from Diplomacy.

I suspect that with Rebellion it will be the same, and once I jump in I won't look back.  As was suggested in the other thread, the real question is what value you'll get out of the game between now and the release of Rebellion.

While you can turtle against the AI, playing pure defense against a human player will get you nowhere.  Veteran players use starbases in a passive-aggressive manner, allowing them to go on the offensive and defeat enemy forces with superior numbers and firepower. 

You might as well just get Trinity if you can find it on sale somewhere.  I think most bricks-and-mortar stores (Target, Wal-Mart, etc.) have it for $30 now.

Entrenchhment was a great addition to the game but it may have made single player too easy since the AI will suicide itself on starbases and wastes its own resources building non-strategic starbases.  It really enhanced the online multiplayer game.

Diplomacy didn't do much for online multiplayer and most games end up playing and feeling just like Entrenchment.  Sometimes people will build the Envoy ships and make the pacts.  It may or may not be a big upgrade over Entrenchment if you only play single player, I don't know.  It does add a Faster speed setting to the game and two more AI difficulty levels (which are nothing more than economy buffs).

If your goal is to play online multiplayer against human opponents then you really do need to get Diplomacy since that's where the action is.  But, be forewarned that player counts are disappointingly low.  (We do still have a couple 4v4 and 5v5 games every day or night, though, but you need to be logged on at the right times and you still have to sit and wait for games.)