I owned a 2014 3-door Mini Cooper S on lease, my parents fell in love with it and bought it off-lease so I went out and leased another 2018 Cooper S 5-door.
It's one of the most enjoyable driving experiences I've had to date.
The trunk with the seats down (40/60 split seats) is big enough for a fair amount of cargo (e.g. 2 sets of golf clubs), and the acceleration, cornering and feel is tremendous.
I really can't say enough about it - it even handles fairly well in the snow and ice here in Canada with winter tires.
The advantage of the Mini is that it shares a lot with BMWs so the quality is impressive considering the cost IMO.
My other car is a 2011 Subaru Outback, which is the long-distance cruiser and utilitarian car for hauling stuff around, but my wife and I both prefer to drive the Mini.
As far as negative aspects of the car - I can't really think of any.
I guess the only one would be that the S has a fairly stiff suspension and it's close to the ground, so it it can be a bit jarring for long-distances on really bad roads.
If you have a child (we don't) in a baby seat, and you have the 3-door, it can be challenging to get your child in and out. But the new 5-door is very practical and it looks virtually identical because they reduced the size of the front doors anyway.
Old Mini:
New Mini: