These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
How about Siege of the Vladstag, the final mission of the first game? It's the final assault, the weakened forces of the Western Frontier, especially after fending off the Iron Legion, deep within enemy territory and far from home, plus a large squad of Tundran Grunts and several Gunships, all against the defenders of the heavily fortified Vladstag, supreme HQ of the Xylvanian army. It amounts to your units killing everything in your way while the Gunships destroy everything from above, all the while Bombers threaten to blow you to smithereens, and along the mission, you have to breach all three of the large stone walls preventing you from accessing the Vladstag. And just when you finally reach the Vladstag... not one, but TWOBattlestations are waiting for you, while two AA Vehicles threaten to eliminate your air support. The resulting frenzy of bullets and mayhem is truly epic... Unless you cheese it by using a sole Mortar Vet orAnti-Air Vetto kill those 4 units.
Demonic Spiders: Pillboxes in the first game, Fighters and Strato Destroyers in the second.
In the sequel, Fighters gain the barrel roll ability which allows them to shake off locked-on enemy missiles. The only issue is there's no cooldown or other reason not to do this all the time. This can be especially unbalanced on the online PvP assault missions where the attacking side have fighters.
Goddamned Bats: Gunships. You generally have your own infantry to deal with the enemy's infantry.