soporj (And me myself at one point) touched on the fact that in fact,eventually one will reach a level in any game that is frustrating as hell.
These levels of course can take forever,however for every one of those kinds of levels,are also ones that are an absolute blast to play but because of that,they just don't last long enough
So what is that one level that you wish lasted longer.
For me,it'd be Green Hills Zone from Sonic the Hedgehog,..yeah I know it's the first level,but it's one of the prettier stages,has a great theme,but the speed of the game makes and difficulty finishes the whole thing off too quickly.
And for a bonus,well how about a Bonus level,more specifically the Tundran Bonus mission in the first Battalion Wars. Between the more powerful units,the amusingly bad accents,and the map isn't hard to traverse.