I've had this machine for several months and in my opinion it produces a very good shot of espresso.
Having worked as a barista in New Zealand (where, perhaps surprisingly, the standard of coffee making is amongst the best in the world), I hope I have a good idea of what to look for. The most important aspect is the speed with which the shot is delivered and the crema. On both these aspects, with the right grind of coffee, the Krups K2 is excellent.
The Starbucks and Costas have lead to a belief in the UK that the milk should be 'foam' or 'froth'. No: what *should* happen when heating the milk is that the proteins are 'stretched' and some of the milk in the jug gains a different density and texture. You are never looking for anything foamy, there should never be any bubbles, even in your cappuccino. For this purpose the steam wand on this machine is woefully inadequate, but then again only a commercial machine can ever deliver consistent pressure for a long enough period. (By the way, if you go into a coffee shop and see the barista pouring your shot first and then heating the milk, tell them to start again! Probably the best coffee I've had in the UK is at the Monmouth Coffee Company in London.)
For those who've had problems with their machines, as some others have said this is most likely down to using the wrong coffee - look for ground coffee that is specifically for espresso machines; having coffee stuck on the head or on the rim of the handle; and/or too much/not enough coffee. There's a reliable measure in the box.
So, with my barista's hat back on for a few moments each morning, I'm very happy with this machine. Recommended.