I like the strong modeling integration of Petrel from petrophysics, seismic interpretation, geology, reservoir engineering, and geophysics. It has the ability to integrate all kinds of data types and make the good benifit of interpretation. I also like the very impressive visual feeling in 3D. It is striking to inset a plot of Petrel into my presentation or paper.
I can quickly test my idea by editing the model, run simulation (with ECLIPSE or INTERSECT), and see the results. There is seldom a software can do everything in the life of E&P and also display results as good as for a peer reviewed paper.
When Petrel crashes, much of the hard work are lost, even with the auto saving scheduled for every couple of minutes.
Petrel can't interpolate the property grid from one fault model to another. If I edit one fault model for a little bit, remove/add/edit some faults, for example, I have to do the property regeneration or interpolation by my self.
The help document is not very clear. Sometimes it is very hard to find relevant help manual.
It seems Petrel has not handled very well with truncated faults (in saving the model and send to ECLIPSE for simulation).
If you really want to understand the subsurface in 3D, you need Petrel, the amazing integrating modeling and interpretation tool.
Geomodeling: seismic interpretation, structural modeling, fault modeling, and property modeling (variogram analysis and petrophysical modeling). We use it to do basin-scale characterization with production and injection wells.