I have a very large collection of OPI nail polish. Compared to $2 shop nail polishes these are amazing. Personally my nails have trouble getting nail polish to stick and not chip but normally I'm pretty fussy and change my nail polish regularly. There are sooo many colours, its so exciting to choose which ones I want to get. Personally I don't think they are worth the $20+ from farmers etc but you get them cheap at makeup bucket sales, ebay or I use candygirl.co.nz and they have a large range for around $18 and they are super fast and nice :)
The nail polish does not thicken which is a massive plus (except the shatter) and normally requires two coats. The colours sometimes fade to a lighter colour but with a top coat there is no problem at all.
Love this polish. It goes on smooth and streak free. The brush is soft and wide enough to cover my nails in 3 strokes. However it does tend to chip fairly quickly.