Pros:

VERY high amount of detail in the first 2 maps in particular.
decent challenge early on. 
fun design and interesting layout.
felt very much like a "secret military base". 
finale effects were interesting to say the least.
story element was refreshing I have to say i was quite interested in what the tomb was going to look like.

Cons:

a bit easy on the finale. 
not quite as much detail after the 2nd map but still a higher amount than most campaigns.
no real "ending".

Conclusion:

very good campaign ya got here! story was excellent and never expected the *SPOILER* combine themes to be there. still the worst part of the campaign was the abrupt ending, if you're still interested in working on it then i would suggest some sort of alien abduction, otherwise this ones gonna be a keeper! also would like to say this is probably in my top five campaigns now

looking forward to more from you. perhaps a sequel taking place on some sort of combine world? *hint hint*
EDIT: ok i read the little information page you made for this campaign and i have to say... how were we supposed to know that? I have seen 2001: A space odyssey and frankly that's the first thing that came to mind when i saw the monolith but when you throw the combine in the mix it just adds to confusion.... just felt like saying that it doesn't have any effect on the campaign itself.