Directives also contain a minimum set of regulations that must be implemented by member states. States are free to expand upon them though.
For example, the Tobacco Products Directive that was recently transposed in the member states' law regulates e-cigarettes and vaping products. Some of the minimum requirements:
Tanks can't be bigger than 2ml (thanks, now I have to fill my device several times a day)
Advertising banned (So existing smokers can't find out about them and maybe not die from smoking)
All products must submit a pre-market report to legislators detailing the device, liquid and it's specs before going on the market. (To make it harder for small companies to compete with tobacco and pharmaceutical companies)
Liquid for e-cigarettes cannot be of strength greater than 20mg/ml (so that new vapers who are trying to switch from smoking cannot get enough nicotine)
Refill bottles can only be sold in bottles of 10ml (great for reducing plastic waste that is....)
Ban on sales to under 18s (good)
The UK has done a light-tough implementation of it, only sticking to the minimums requested by the EU. Other countries have gone much further by doing things such as banning cross-border sales etc.
There are also provisions within the TPD that say that if 3 member states choose to ban e-cigarettes outright, then all member states will be obliged to follow suit.
So, directives are sort of a minimum set of rules that are mandatory for EU member states but the actual legislation is enacted at a local level.