I am not one to plonk a five star rating on a product just to follow the crowd (as my can readily be seen from reviews on other products). So, to get the five stars from me, I have to really REALLY like the product.
As other reviewers have already noted, the HD 205-IIs are remarkably good value (less than £25 at the time of purchase in December 2010).
Having replaced 3 old sets of headphones (Sennheiser HD-450; Panasonic RP-HT230; Sony MDR-?) with 3 new sets (Sennheiser PX100-II; Sennheiser HD 205-II; Roland RH-50), I've had some listening to do.
My preferred listening is classic rock (e.g. Pink Floyd; Marillion; Genesis etc) with some softer acoustic material thrown in every now and again.
In short, the HD 205-IIs beat the pants off ALL the 3 old sets - even the old HD-450s which, from memory, cost more than £40 more than 15 years ago. Top and mid ranges have excellent clarity and reproduce decent stereo staging. The bottom end is well defined, although a few *may* find the bass just fractionally too prominent.
I personally found to HD 205-IIs to be better than the slightly more expensive (at the time of purchase) PX100-IIs. In sonic terms, the HD 205-IIs are the most enjoyable headphones I have ever owned (distinguished from listened to :-)).
The only minor annoyance is the head band. For obvious reasons, the phones are designed to clamp pretty snugly on/around the ears. In truth, I'm finding the fit a bit tight but am hoping to get used to them and that, in any case, a bit of use will see at least a touch of the tightness ease off. But, this issue isn't so big that it affects the five star award.
NB: The packaging... This is not about the product so the rating is unaffected. Sennheiser would be wise to take note that opening the packaging for these headphones is a nightmare. Even with care, it would be very easy to cut yourself (as indeed at least one other reviewer has). Sennheiser, change it - PLEASE!