PianoTeq is astonishingly good, but you must be willing to spend time learning to understand it. If you know nothing about the various elements that contribute to the sound of a piano, you may find the many parameters overwhelming. Often, since each parameter is added to the effect of another, one must edit several of them in small increments to achieve the sound you want--increasing the hammer noise, for example, you may also want to decrease the hardness of the hammer.
The interface is in many ways excellent: you can see almost every parameter easily. However, for a new user, the layout may discourage an understanding of the ways in which the parameters interact: often, you may want to make changes in several windows to gain a specific sound. To increase the length of the sustain, for example, a single edit in one box will almost certainly require edits in another.
And a suggestion from the Pianoteq users' forum: Try setting Dynamics to somewhere between 30-40, instead of the default 60. The result will be louder soft velocities that retain the harmonics of soft hits. Then experiment with various other edits. You will be better able to hear the changes, and be able to hear how velocity affects each parameter.