It took me several months to finish the campaign, but I can definitely say it was worth the time.
I downloaded it a few days after the initial release, so I probably don't have the lastest patches and additions. No crashes and showstoppers for me, everything worked just fine.
It's surprising to see how many people are complaining about the grammar. It's not difficult to figure out the meaning of the writing, come on, it's just a few minor grammar issues. How many people here know how to pronounce this 'szierbiecz' tongue-twister missile?

The first mission was quite frustrating. If I remember this correctly, you end up with a few percent hull integrity and have to fight two cerberus guys that can kill you with a single shot. I tried to outmaneuve them and call in a support ship at a safe distance. Didn't work.. Went for the node and was surprised that I couldn't jump out.
As for the difficulty: Some missions were particularly frustrating:
-I failed to save the Nirvana several times, because it gets swarmed by capships which have enough beams to take on half a dozen Nirvanas.
-And in the last few missions (though they were definitely epic) it was really difficult to keep all my artillery ships alive. A few contentrated shots of nightmare beams and the mission is over.
-And this mission where the Neya lures the nightmares into a trap next to a station (I can't remember its name) was not the easiest, because the nightmares got the subspace perturber every time, while I had no clue which ship or object I am supposed to protect. It would't harm to add this to the missions' objectives.
The good
-Well-developed missions, especially the bigger battles. Nothing seems rushed or unpolished.
-New enemies
-A few innovative things I haven't seen before in any other mod
-Missions on planetary surfaces (woohoo), even a city!
-Each time you think things can't get any worse and you just took down an enemy force that outnumbered you by far, it gets worse and even stronger enemies show up. Two thumbs up for the checkpoint system

The bad
-Quite a few missions are mainly about shooting the beams of dozens of enemy capships. I found myself, all three banks of secondaries filled with penetrators, hovering below a support ship, rearming without pause and dealing more damage than the haphazard artillery was able to deal. And when someone shoots down the support ship, effectively cutting your supply of missiles, you find yourself on the losing side soon.
-Penetrators are really superior to the tongue-twister missiles by far, so I dropped Szierbiecz quite early. Szierbiecz has only half the range and is quite lame for disarming beams, against Gualis it is effective but you can't arm your fighter with more than 12 of them, so it soon becomes a 'shooting and calling support' dance when you have to deal with dozens of Gualis.
-I quite liked the storyline, but it reminded me in many ways of FS2's vanilla campaign. Agressive invading aliens. A deranged human leader staging a rebellion with a strong interest in those aliens. I anticipated the moment where a Sathanas-like juggernaut would show up and I wasn't disappointed. Still it's a very good story, but I found it a litte ... predictable..
-When I went into nightmare territory with the SOC stalker, I expected to find more than just derelicts that I was supposed to scan. Here the plot could have been thicker and better narrated.
-Please add a 'press x to skip cutscene' option. It gets boring if you've forced to watch the same cutscene a dozen times.
-Frenchmen might find the naming of the Merdarion hauntingly appropriate

Last but not least, how can I get all those achievements? I only got 7 out ouf 32(?), guess that makes me a lame pilot

Is there a list of them somewhere?

I can't wait to play the sequel!