I've found that acrylic paints (I use Tamiya and Citadel) are nowhere near as bad as Humbrol and Revell enamels
from the point of view of evaporation/spoilage, partly due to the design of the containers. With the aforementioned enamels, excess paint builds up around the tin lids and prevents them from sealing properly (scraping them clean with a modelling knife sometimes works, but not always, and is VERY messy!).
Enamel paints also tend to react strangely when they start to evaporate, often all the solvent solidifies into a rubbery top layer, leaving the pigment at the bottom; whilst metallic paints tend go lumpy, gelatinous and "gloopy".
I've lost count of the number of enamel paints I've had to throw away, many not even half-used, because of this.
This is one of the main reasons I'm switching to acrylics now (after painting with enamels for almost 4 years)