What kirsteyj87 said:
Regulated mods contain electronics and circuitry, stuff like battery overcharge protection, timeout's to stop you firing the mod for too long, little LCD displays to show you information about your resistance and your wattage, safety measures to stop you firing on a coil that is too low resistance, or has a short circuit somewhere in your build, some (like my kbox 70) contain built in batteries so you don't have to worry too much about whether you've got the right batteries. You can just lean on the mod to do the right thing.
An unregulated mod, is a tube with a battery in it, a switch and a 510 connector for your atomiser - when it comes to making sure you don't have a short, and that your build is correct and safe for the particular battery you have, you need to be a lot more careful and considered.
In case it isn't obvious - I'm not brave enough for an unregulated mech mod
I like the safety that the more complex devices give. I can't say how the vape differs though because I have only used regulated mods. I know that some people swear by mech mods...
Probably worth saying that even regulated mods are only as good as what's in them, so it's worth buying a good quality device from a known brand and vendor.