With regard to the "Those dirty Germans built Stone Henge first!" achievements: I like them. They give a brief idea about how the other players are doing, and add some nice flavor to the game. That being said, I would prefer they be along the lines of news broadcasts (like MOO2). Feel more like news from afar, rather than a big deity telling me to stop building the Great Wall of Italy 
With regard to the "List of the top five most militaristic players": I don't really like these, just because they tend to feel pointless. You usually get a better idea of what is going on from just checking the various menus or even looking at the border. That being said, I don't really care if they are in or not. And, if Elemental's ratings system actually has meaning, this could be fun.
With regard to the "Impale five enemies with a single ballista shot": I DO like these, but only if they are done properly. They should either be things that happen over the course of gameplay (Bad Company 2's online achievements are a lot like this) or things that encourage you to try new and exciting things (the recent update for Half-Life 2 encouraged me to try Ravenholm with only the gravity gun. Was a VERY fun experience). But stuff like "Jump off a cliff ten times" or "Knife fifty people with gatling guns" aren't really my cup of tea. Unless it is the kind of game where you are encouraged to do crap like that (Just Cause 2
)
As far as unlocking stuff with global achievements: I am perfectly okay with that in FPSs and the like. But I am pretty sure Elemental isn't the kind of game that would really benefit from (or even work with) that kind of system.
Per-Character "Achievements": These would work great. I love them in the Total War series. In fact, I would be pretty surprised if a feature like this isn't going to already be in the 0-Day patch or capable of being added through scripting. Every time you massacre an enemy (maybe one unit kills off 50% of the enemy force in tactical), you get a chance of getting a trait.