The majority of the enemies listed above won't really cause players any real issues when faced on their own. However, they can become problematic if faced in large groups, or in conjunction with other enemies. Even Menials can cause problems if they sneak up on you, so just because something is weak, it doesn't mean they can't cause problems.
Strong/Very Strong Foes
These are the real tough cookies, for different reasons. Hardfangs have a tendancy to rush and can cause considerable damage, while Widowmakers are effectively walking battle-tanks. Angels on the other hand, are the sentinel units and can fly around, making them very awkward.