Defense Grid the Awakening/YMMV


 * That One Level: Several of the advanced challenges can get very, very bad.
 * Some of Center of Power's advanced challenges can cause a few gray hairs.
 * Turnabout's advanced challenges (namely Super Grinder and Green Towers Only) are the point where you are forced into "juggling" the aliens in order to achieve the Gold Medal. Even then, getting that requires precise timing when juggling the aliens, without which these challenges are largely Luck Based Missions.
 * It's nothing that the application of enough gun/cannon towers and construction of a long enough maze can't handle. Try doing the Gun Crazy achievement on Height of Confusion and you'll see why they're just shy of being OP.
 * The Woobie: Many of the places you visit had special importance to the General (where he lived, where his family lived, where his mind was uploaded into a computer , the sites of battles from the previous war ... it's hard to not feel bad for him when you hear his reaction to revisiting those places.