OPI have a great colour range & bring out amazing limited edition sets to match whatever trends are in (eg: movies, colourways etc) so i have a huge collection!
But i have found that if you use the full range (#1 basecoat or strengthener, #2 colour & #3 top coat) then you will get great vibrant results that last for up to two weeks BUT if you use other brand base or top coats your paint will start to chip within a couple of days.
I have also found that when applying colour you need to apply more than one coat otherwise a majority of colours will be slightly transparent or streaky - the second colour coat makes the finish much more even.
Overall i feel they are a very strong product and great quality , they just need to be used with their own range of support polishes or treatments :)
I like the large range of colours OPI offers but I find it no different to the cheap nail polish you can buy, it chips just as easily.