What I've ridden before:
1)  Specialized Sirrus Comp 2005
2)  Friday Folding Bicycle
3)  Gary Fisher carbon hard tail MTB
4)  Some no-name folding bikes from China

The Good:
1)  Beautiful design & construction, absolutely the best looking folding bike out there.
2)  Sturdy & absorbs bumps pretty well for a non-suspension bike.
3)  Versatile - fits 5'4" to 6'0" with the adjustment of the seat, comfortably
4)  Fits in the trunk of my sport coupe!  No other bike fits in my trunk!  Figure a 24"x24" square
5)  Enthusiast following, easy easy resale.

The Bad:
1)  Easy to scratch when you fold and transport - get a good case, or make one.
2)  Heavier than it looks - 30 pounds or so.  Brompton should consider carbon fiber or aluminum.
3)  3 speeds not really enough, get the 6 speed.
4)  The small roller wheels to allow transport need to be made larger, they are too bumpy on cobblestone.  Not the bike wheels themselves, but the transport wheels - you'll know when you see them.
5)  Costly.

Overall:
Great bike, and the only one that really fits in the space I had.  Nice design + "WOW" factor.  But, for the price, I really expect more...