Pros: excellent build quality, detachable cable, comfortable, good bass,
Cons: parts not changeable, carpet in lower highs, too low clamping force (moves on head)
I bought this cans because I needed a pair of headphones for outside mobile use with a normal phone/mp3-player. As such, the design and build quality were the most important factors to decide.
In this regards, the Fidelio L1 is an excellenct choice, as they are beautiful and have a very solid feel to it - everything on this headphone consists of either metal or leather. The leather ear feels very soft and plushy, but not as plushy and comfortable as for example the Beyerdynamic DT series' velour pads - they do get warm on the ears after some while, but that is a general disadvantage of non-pervorated leather materials. The clamping force is quite nice after some time, but it could be a bit more of it, as they move around on my head when I do rapid head movements - they tend to either slide into my neck or into my face - this is one of the major disadvantages in my opinion.
They isolate quite well against the outside world, considering the mesh structure on the outside of the earpads. Sound leakage into the outside world is also low - up to no-existance at my personal hearing levels (I asked a friend sitting 50 cm away from me in a quiet surrounding).
However, this cans aren't the most physically portable out there. The cable is detachable (it comes with 2x 1m long cables, one of them with a 3 button cable remote), but it tends to coil itself up and to entangle horribly. Tee soft bag feels good put doesn't protect the cans at all - it's just a means of transportation. It's quite bulky to transport on its own because it can't be folded up like some portable cans do. However, the ear pads swifle, so they can be placed around the neck and get out of the way easily.
They sound like typical semi-open cans, without the feeling of being closed in, but not with a particular amazing sound stage. The bass response is rich without being over the top and relatively warm sounding - the bass blends well with the low mids without sound peaks, but lack a bit of really deep bass in my opinion. However, there is a "carpet sound" right at the frequencies of normal human speech - that leads to a relatively long time until one gets used to it's sound, but it doesn't affect my listening experience too much once I get used to it. However, this characteristic is this pair of headphones' major flaw and could be the major reason not to buy this pair (at least, not as the primary one) - but you should check for yourself if you don't mind it, like it or hate it. The treble is there clearly and not too aggressive or pronounced.
They are very easy to drive, because the have "just" 32 Ohms impedance (I'm used to 250+ ohms from my Beyer and old AKG cans) and are quite efficient. They don't profit from a headphone amp at all (unlike the former named ones) and can be easily driven off of any clean (they pick up hissing noises quite well, but not as good as IEMs, of course) "normal use" sources, like phone and mp3 player headphone jacks.
Overall, I use them as my smartphone pair of headphones. They are fun to listen to but not too revealing and detailed. They are exceptionally good for a wide range of musical genres (I listenen to Prog Rock/Metal, Classical, Rock and Metal, Jazz and a variety of electronical genres, in this order) and for multimedia use. The major setback with these is the uneven response I described as "carpet", but I get used to it in about 5-20 minutes every time. I wouldn't buy them for the 180€ they cost on Amazon; watch out for used ones or special sales for about 120€, that would make a good deal that I could recommend at least trying for everyone.