There are various theological reasons why the Roman Catholic Church and certain orthodox Anglican dioceses do not ordain women to the priesthood, and what it boils down to is that Christ chose men only for his ministry and the Church is simply following his model for the Christian ministry. This is somehow construed by the laity (especially the ones who do not even attend church) as an issue of "equality". There is no doubt in anybody's mind that men and women are "equal", but they are not interchangeable, although in this gender confused generation I am not surprised that people can confuse the two anyway.
I think you are asking the wrong question. The question shouldn't be "what's so great about being a priest?"; the answer to that question is irrelevant to this topic. The question should be what can men do that women cannot which makes them uniquely qualified to be priests? There were many answers to this question in the early church. For example:
1. Men could read and speak about the Torah, having been taught to read and memorise scripture since childhood. Women were not educated, would have received no instruction on the law, and are unlikely to even be able to read.
2. Men were allowed to speak in public and teach Torah at the temple. Women were not allowed to do this.
3. Men could talk to other men on the street. Women had to wear a veil and look downwards as they walked in the street, never daring to approach an unknown man.
As we can see from looking at the culture they lived in and the restrictions placed on them by the society they were serving in, there were many things men could do that women could not which would have uniquely qualified them to be priests. With those reasons gone, now that we have advanced as a society, women are educated, and are allowed to interact with men, does it still make sense to refuse to ordain women? At this point all we have is an appeal to tradition.
I'd like to bring up two points to circle back towards theology. First, I want to point out that Jesus criticized those who followed the law blindly without stopping to think of what the purpose of the law was. In Mark 2, for example he corrects some teachers of the law about how they have turned something that was meant to benefit people (the sabbath) into something they are slaves to. He is encouraging them to forget about the letter of the law and understand its purpose instead. If we are to do this with the law, how much more with tradition? We shouldn't follow tradition blindly, we should understand why we follow the tradition and be aware of when it is no longer appropriate. Do we follow this tradition because there is a deeper theological significance? or did we create theological structures to support what was a practical decision of the early church? Namely, the decision to ordain only those who were educated, had the ability to speak publicly, had the right to engage other teachers of the law (both Christian and Jewish) in discussion, etc?
Secondly, I want to point out that the first century church faced a very similar dilemma. The big debate around the time the new testament was being written was over circumcision and some of the dietary laws. It was a question over whether we should continue to blindly follow tradition or whether changing circumstances have rendered such traditions obsolete. As we all know, the apostles chose to discard tradition. Although some complementarians do have a strong theological foundation for their belief, I get the impression that most of them would have been the "we must stick to tradition" types that Jesus and the Apostles sided against.
We offer that women can choose a religious vocation (for those of you on the left, that would mean Sisters, or Nuns) just the way some men choose to be religious (monks).
No one can choose a religious vocation. Well, they can, but then you recognize them for their ineffectiveness. Rather, people are called by the holy spirit to a religous vocation. One of the challenges facing complementarians is the fact that we see strong evidence of women being called to the priesthood constantly and we see them abandon the church they love and grew up in, heartbroken, in order to pursue a calling that their church is holding back. Complementarians, though well meaning, are attempting to hold back the work of the holy spirit. It will not be held back; they'll simply find themselves on the wrong side of history and in dying churches that failed not just to keep up with the pace of social change, but to keep up with what the holy spirit was doing.