Call me crazy, but I like BF4. It not too hard, not too easy... You have enough advantages that, if you play it right, you will never lose a clash. There's plenty of terrain and unit relationships to help you.
BF1: Way too simple to be fun. Still, the tutorials in this game are some of the best I have ever read.
BF2: Still too simple...
BF3: Too hard...
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BF17: WAY too hard (Gulcasa).
BF28: WAY too hard (Gulcasa).
BF32: This one has decent difficulty. I thought it was pretty fun. Make sure you give someone the headgear item if you have it (Void ailments). And GEN up items. And use your terrain advantages (Bridge, Road, Town, Water). For the last part, Gordon is allowed to die (Not Kylier, Yggdra, or Milanor). So make sure you let him. So for your opening move, move Gordon to the town and attack the imperial knights. After that, Aegina and Gulcasa will come after the rest of your team. I put Durant on the top-most bridge and Nietzche on the water. You can survive for a long time w/ those 2. Winning will be easier that way... If you want to try and steal their items, Milanor needs MAX morale. He'll die if you don't have it.
BF44: The last part of this is difficult b/c Gulcasa is so strong. For me, Yggdra and Milanor died many times before winning...
BF47: I'm not sure I like this one either. Basically if you choose easy mode (Kill Astarte first) then winning is simple. If you choose hard mode (Kill Nessiah first), I can't win. It's just too hard. HIGH status PLUS regeneration?
All of the BFs you guys mentioned are REALLY difficult. You guys must be hardcore gamers or something.