Ultimately, I think the campaign was great. There were a lot of issues in it though that hindered the experience a little, but the overall effect of the gameplay and missions made the campaign stunning for me.
Beyond that though, I feel it was very rushed. there was a lot they tried to cram in and it loses impact on the player. For instance, they pretty much tell you right off the bat that Cortana was going rampant, they made it an issue to the player immediately. Though because it happens at the beginning, there isn't much to make the player care yet. Instead, had she tried to keep quiet about it and you start to see the effects before she finally reveals it in the midgame, it would have been a solid dramatic moment, and would have carried a lot of weight. I truly felt that content and missions they were showing in the beginning (wakening the Protheans) really belonged in a midgame setting.
Another issue I see quite a bit is the plot hole. How does Cortana know all this? How do they know that's the Didact, even though it only says so in subtitles and he never specifically states it? How does Cortana know deactivating these objects will clear up comms? I know there are valid reasons for why they know these things, such as data over feeds, but the source of all this info is never specified, the info is just stated as fact.
The last issue that I personally find is that you seem to run out of ammo, a lot. In a single firefight I could easily end up going from full clips to no ammo in either weapon. I can't tell if enemies take more ammo to take down, of if weapons fire faster, or just lack of ambient ammo, but it disrupts the pacing when you are constantly looking for another weapon because both of your current weapons are out of ammo.
Now, as far as pro's go for the campaign, I loved what they did with Master Chief as a character. before he was a silent individual, but now they really show that he has humanity, they there is a person under the helmet. I also like how they leak information about the Forerunners and ancient Humans. Ultimately the story they told, I enjoyed. Even if it had flaws, and its presentation was rushed, I found it exciting.
Another pro I found, was how smooth the controls were. Everything felt right. You felt like you were a super soldier in a half ton suit of armor, yet were incredibly mobile. There was a certain grace and fluidity in the movements that felt perfect.