Depends on how you do it. Check my Warriors of Chaos log for a good example of an army that is nearly entirely metallic paints. For the most part, painting metallics isn't really that different from using regular colours aside from the fact that they are somewhat thicker and using too many layers will obscure detail quickly. Your best bet, in my not so humble opinion lol, is to mix up a bright version of the colour you are going for and then use washes, either GW washes or your own homemade ones, to darken the paint down to where you want it. My entire WoC army has been painted in this way and it works quite well.
If you wish to go for the layered technique where you build up to the lightest colour, keep in mind that milthril silver is as bright as it gets, don't plan to go past that. Also, try to thin out the metallics with flow aid or something similar as water won't do it properly which will really show up in the smoothness of the paint.
The other thing to remember is that you MUST have some non metallic paint in there somewhere, even if it is just black shadows or a bit of cloth somewhere to break up the metallic areas. Otherwise it will be 'too much' and won't look right. And this has to be on the model itself, not just the base. This will add more realism to the model and will help draw the eye a bit more.
k::victory:
