The visual quality doesn't offend my eyes - as it does some...
In my opinion, it's quality will be a function of it's storytelling. Whether this is a good film or not? The jury is still out on this (most important) issue. I see no particular linkage between this and expensive visuals. There are plenty of examples of expensive visuals and s^&t movie.
If this movie rocks, then word-of-mouth within the WH40K community will ensure its success. The reverse will be true. I imagine this dvd will be sold at GW stores too - people will buy it regardless.