I've been pretty satisfied with Hard (only played RTI so far, though). The troops on both sides tire appropriately, and morale erodes and breaks for what seem to be the right reasons - fatigue, clear mismatches in numbers or capabilities (troop/weapon types and techs such as canister shot or rank fire), or flank/rear attacks. I haven't played that much yet, but I have yet to win a battle as the underdog (not that I'm the paragon of TW tactical genius or anything). I typically win (albeit "close victories") when about evenly matched, though, especially when defending.
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