This game is WAYYYY too easy... I finished it on my second attempt...
Maybe I just got extremely lucky or something... but didn't feel like it.
Just buy all the potions you can, and you'll be fine. And don't use magic (except heal).
There is no instant victory if you destroy the castle, but there is if you steal the enemy's flag. Your units need to reach it and they will carry it back.
There seems to be a problem with the "seconds remaining" calculation after a fight. I finish a fight with over 7 minutes left, but it tells me I have around 200 seconds remaining...