Properly understood, the liturgy is the sacrament of our conversion to God in Christ, which results in our being empowered to transform the world in the power of the Spirit. Prayer, praise, proclamation -- all play a role in the process of sacramental conversion, but when any of them is emphasized more than the others, our liturgies can fail to achieve their purpose and leave our congregations unchanged by the experience, which has long been the unfortunate norm in our parishes. Then, people gather out of obligation, or enjoyment of an aesthetic experience, or some similarly mundane motive.
I agree with Michael that preparation of our liturgies ("the work of the people") is essential, but I also agree with his implication that few of our liturgies are well prepared by the people who participate in them. In my view, I think Christianity's adoption of the mandatory sabbatical celebrations has resulted in our taking the liturgy for granted and our passive acceptance of an hourly ritual.