Exploratory testing is hard... if the product is difficult to use
1.
A product or feature with many days worth of nitpicky bugs could be "at risk" because a tester might be distracted by all the easy bugs and not spot a workflow (usecase) that is important.
2.
Features that are hard to use or configure might get missed. Consider a product with 10 major features, and 9 of them take 1 day to configure and get real data back from. The 10th requires 10 days to configure (it requires the sum of all other features to work) plus another day to collect data. In this case the testing is probably going to be interrupted (a customer escalation, a project date boundary, etc.), making it easy to forget to come back to feature #10.
Here are some ideas to mitigate these risks, do you have others?
-Use written testcases for these features. (Might be hard to know that you will hit problem 1 ahead of time)
-Do use case based testing, and track your results by use case instead of by program feature. (I want to try this idea on my current project, but have not yet)
-Put the best most "bloodhound" minded tester on that one problem area, and assume that they are up to the challenge.