After 10 ingame years of human mode... some observations:
Like the person above, I've only ever (10 years, 3 different fortresses) been invaded by night creatures. Nothing and no one else. Twice I got the message 'an army is invading from the north!) but no army actually showed up. I've also never been offered to become a barony so that might have something to do with it.
Funny thing is, my human civ is at war with another human civ and THE VERY INSTANT I retire a fortress and a baron / nobles are appointed it starts to get sieged by other humans like crazy. Like, the very next month (this happened with both my retired fortresses, both the same human civ). Sieges about twice a year.
I enjoyed my humans immensely, BUT: the inability to join a garrison, coupled with the harsh exp penalty for combat skills without garrisons, was too harsh in my opinion. Dwarves get to become legionnaires, why don't humans? I spent year after year training up my soldiers in a library and it was soooooo much micromanagement to get them anywhere. Sure, the standard guilds offer some xp bonus to some skills, but that's more micromanagement and afaik you can only get one combat skill boost from a guild. Also no stat boosts. Seriously, humans need garrisons.
I also found the guild skill boosts to not be intuitive at all. Why do farmer guild members not get any grower skill bonus? Or clothiers no clothesmaking skill bonus? And merchants get 3 different weapon skills... huh. This was very confusing. I ended up not using the guilds at all.
That said, the tech tree was super awesome, lots to discover and something refreshingly different from vanilla dwarf mode.
Just my 2 cents in case someone wants to keep working on the mod at some point in the future.