I have liked the game all along.  Crusade just makes it even better,  The improved AI is worth it all by itself.  The rest is just bonus content for me.    But there are some very interesting additional mechanics.  Diplomacy is much better as well.  And don't forget the Fleet and Faction Builders!  

I agree with the 9.5 rating.

Depends, on what is annoying to you.

Things such as tech tree layout are still somewhat in flux. I would wait and see another month or so before giving a final verdict.

SD is taking a more conservative approach to their game mechanics now. Which is good and bad. To be honest I am actually missing the earlier version of gc3, when you could terraform all salvagable tiles with sufficiently high tech and doing other ridiculous stuff. I don't think you can still make 1k beam damage ships either for example. The upside of this is, that it is easier to balance since there is a lower potential for exploits.

I think this is the actual nature of the apparently better ai.

I play galciv III every now and then to check on the progress of the game.  I am waiting for the game to really feel mature before I commit a lot of time to it.

The game has improved significantly since lunch but imo there is still a lot of annoyances in the game, even as of Crusade.  Just now I wanted to try and play a campaign but cant because of a max population bug that makes all campaigns unplayable ( Check my recent replies for reference ).  At the moment my main issues with the game are not so much about the game or its mechanics but rather bugs,  UI annoyances or lack of some specific options.

Yeah, there are some serious issues with cost/benefit on some stuff.  Without leveled flats, they're really not worth much to start with, and you need a huge amount of production to make the upgrades valuable in the short term.  They eventually pay themselves off, but 2.5% takes a while when you could have done Aid Research for the same cost, and not spent a resource on top of it.  That your planets are probably going to be really good at producing buildings compared to how well they can produce research just makes it all the worse.  You can do a cluster around a Space Elevator, more than double your production, and make those poor science buildings take twice as long to pay off.

Your ability to make a planet "better" at science in a similar fashion is somewhat severely restricted.  These Space Elevator clusters are also smart to build on every planet, because they greatly expand the ship production capability of the planet, are downright necessary to actually build those science structures without taking hundreds of turns, and end up farming more science or money in the end anyway.  More ship production also being a method of gaining research and money yet again compounds the issue...

The plus side is that planets don't go from taking 20 turns to produce a 1 attack ship, to single turn producing a 6000 attack ship.  I wish that were a flagrant exaggeration.  The scale up is unmanageably exploitable in vanilla GC3, what we've got is a far superior progression, it's just got some major issues at present.  Hopefully soon to be fixed issues...

I'd hold off a bit. The list of issues from launch has been long and while updates are coming frequently they have not addressed many of the bigger issues. For example if you planned on doing any multiplayer at all I'd hold off until they release a patch that fixes the many issues first.

I'm not playing anymore till tech stealing can be turned off, it is far too easy for techs to be stolen (especially the ones the so would take too long to get on their own)

yes yes yes and more yes.