I think (other than safety) the two most important things I look for when buying toys for my kids is;
1. Annoyance factor - the toys cannot be too loud, difficult to turn off, or messy.
2. Re-play-factor - I have to ask myself if this is a toy that they would play with once or twice and be done with it, or is it a toy that they will play with for a long time.
Strangely enough, my kid’s favorite toys are usually the most simplistic ones. (Hula hoops, dolls, mirrors, etc) Every time I've bought them an elaborate toy, or a remote control car, it's only interesting for about a day or two.