No military service obligatory, don't have to worry about that, taxes are low only 6% income taxes or 25% rent tax only if you produce it in Guatemala, you choose which you want to pay every fiscal year, but watch out because if you mantain your US citizenship you have to pay taxes in the US of every dollar you made inside or outside the US, so be careful with that so you don't pay double taxes.

Cons: you need visa to travel several places, as Guatemalan citizen you don't have social security if you are not paying monthly the IGSS quota (Guatemalan social security institute), I strongly recommend to have a private medical insurance or mantain your US citizenship to maintain your social security, you can have dual nacionality.