I found that the IsCritical attribute is always false when reading an MPP file. Is that because it is a calculated field? Is this something you plan to implement in a future release? One thing that is bothering me is that all these fields are exposed and available but they are providing incorrect data, like StartVariance, FinishVariance and TotalSlack. I can understand that reverse engineering MSProject calculation is probably no simple task but you should not expose them if they are not supported. This is very misleading since I don't see this documented anywhere in your site. Maybe it is something that is only supported in specific formats, I am not sure. But you really need to have better documentation of what is functional and not functional.
These are all things that might not be immediately obvious when evaluating your products and could be giving an impression that it does support those properties when in actuality it does not. This is misrepresenting your product to show more functionality than it truly has, and might upset people who purchase this only to discover that they just wasted their money on something that will not work for them.