I am a nail polish junkie and I must say, OPI is by far my favourite nail polish brand! The consistency is nice (not too thin or too thick), and the colours are quite pigmented (depending on the colour itself). One of the things I like most about it is that they are also easy to apply and also dries quickly in a reasonable amount of time. It is also fairly easy to remove the nail polish (apart from their glitter polishes, which are just as hard to remove as any other glitter nail polish) and they don't usually stain your nails (but again, this is dependent on the colours, as some colours are more likely to cause slight staining than others). I always apply a base coat and a top coat, and I find that my OPI nail polishes usually last for about a week without chips. However, this will be different for everyone as it depends on what kind of jobs/activities you do that will affect your nails.
The only thing I don't like is how it is so hard to pick which colour to buy, and then to decide which colour I want to apply as well (since there are so many colours to choose from in their range). To be honest, that's about the only thing that I don't like about the OPI nail polish range, if that even counts at all! If you can save up for one, I would really recommend trying it. I did, and now I've never looked back! :)
I have been buying OPI nail polishes for years and now have far too many to count! Out of all the nail polish brands I have tried, they're still my favourite. I find the consistency is great, smooth and not too thick or thin. They apply easily and have a nice brush tip which delivers a good amount of varnish, I usually use two coats with OPI to achieve a thick, solid colour, although some of the colours you can get away with one. The finish has a nice shine even without a top coat, although I still recommend using one to keep it looking good longer. The colour removes easily and I find that even without a base coat, I have never found they stain my nails which is great. Pricewise, you can often get OPI polishes on special at makeup clearance sales, NZ Sale, ilovebeauty.co.nz and OnceIt, which can save you a fair bit as the individual price tends to be a bit higher than some. One of my favourite things about OPI polish is the branding, the always have such cool names and colours! Overall I would definately recommend OPI.
Tips: The bottles last forever, keep them in the fridge especially in the warmer months to stop the product thickening. If it does, try putting a few drops of nail polish remover in it to help thin it out. Also, if you're not too sure if a colour is really you, try the OPI minis! They're great value for trying out some of the fun and interesting shades OPI comes out with.