I had one when I was in Singapore, it was a standard Cooper. It's a decent car though quite expensive for what it is.
Bought another one last year, it's a JCW version. Used to thrash the living daylights out of it from the day I collected it from the garage. My favourite thing to do with it was to find out how fast I could take a corner with it on all those Welsh country roads without losing any grip. Every time I drove it, I've never changed gears below 4500rpm. Surprisingly it was a very reliable car despite all the hard driving it went through.
But after 3 months of having it, it became just another car.... you get tired of it after awhile and start noticing all the flaws.
The downside to it is the headroom and space inside is quite poor for a car its size. Strictly speaking it is a 2+2 seater. Refinement is not great considering the price.
If you are buying one brand new, then watch out for the expensive options....... the list of things you can get is very long but most of them are quite pricey.
After 11 months of use, I got a company car, so I handed the keys to my gf who drives it these days. She loves it more than I did and I think she drives it too conservatively. Insurance for a 20 year old female with 2 years of NCB isn't all that bad around £1500 per year for insurance with me as a 2nd driver. If it was a standard Cooper version it would be around £700+ only.
The thing that does become expensive is obviously the petrol if you drive it like I did and the maintenance is, spare parts can cost a bomb at a BMW dealer. Servicing is definitely a pricey affair and so is the consumables like the tyres and brakes.