These are my least favorite scenarios for Arena.
I'm posting from worst to least-bad.
Sainte-Mer-Eglise (completely random and not even fun)
Pegasus Bridge (2 card starting hand? Come on)
First Assault Wave (Lots of fun, but not good for competitive play)
Arnhem Bridge (also fun, but even less good for competitive play)
Sidi Rhezeg Air Field (let's try bad terrain, empty flanks and no room to maneuver!)
Knightsbridge (let's try NO terrain!)
Panzers vs Grants (let's do terrain that doesn't really serve a purpose and put exposed infantry against the back line!)
1st Armored to the rescue (let's put armor in a no retreat position, give them useless terrain and no units on one flank)
Vassieux (4 medal map, with a potential 2units dead before they get to make a move...)
Pointe-du-Hoc (can become a complete stale mate where both sides just wait for BEL, Barrage or Air Power)
Mont Mouchet (2 medals for killing one unit?... in a 4 medal map...)
Flanking Maneuver at Bir Hakem (let's put all the fun stuff behind barbed wire AND mines - and keep the rest of the map completely open, so we never get to use it...)
Escape via the Coastal Road (let's exit this map ON A ROAD, chaps...)
The keen eyed observer will have noticed that I really don't like a lot of the desert maps, but I will say that Hellfire Pass is one of my all time favorites, so it's not actually the North African rules as such, just the map layouts.
Maps not on my list, but mentioned by Wiking.
Sugar Loaf and Half Moon - This is sometimes extremely unfair for the Japanese, but they're not without options - if they can use the caves and their own artillery to some effect.
Wake Island - actually one of my favorite maps, though it can be extremely tough for both sides. But both sides have options - and it's possible to win as the allies, even if they lose their artillery early on.
Slopes of Mount Austen - while this can be very unfair - there's always ways to attack for both sides.