Pros: Excellent Mids and Highs, crisp detail, easy to drive
Cons: uncomfortable out of box for long listening periods
I purchased these after having realized that I'm not a big fan of the Sennheiser soundstage. I was looking at he HD595's, but similarly to the 555's, I found them to be a little too broad of a sound for me, without picking up on detail. I heard Grado's prominent mids and respectable high's would be good for me, and I fell in love with the sound immediately. The high's at first are a bit too forward maybe before wearing them in, but they soften up with use, and the bass is subtle and punchy without being boosted or muddy (I find the bass to bleed too much with the sennheiser 5x5 headphones, and have never been fond of overdone bass in the first place).
NOW...the cost this greatness comes at for me is a dilemma regarding comfort. The bowl pads these come with are on ear, and not well cushioned. I know some people do not mind this, but I find after 20 minutes or so of listening, my earlobes begin to ache from the uneven clamping on them. There are replacement pads, and various mods to remedy this however.
In general, I find the grado's to provide excellent clarity, respond favourably to hardware EQ modifications, and are VERY easy to drive. Generally these sound fantastic with rock, metal, and some folk/bluegrass. A lot of people do not prefer these for classical, but I think that depending on the type of classical music, these can be very good (Classical romantics such as Felix Mendelssohn, as well as more moderns like Debussy and Berlioz sound great).
If you're looking for an affordable set of phones, and aren't just looking for something bass heavy to complement your Michael Bay DVD collection...I couldn't recommend these enough. These headphones provide me the experience of finally being INVOLVED in what I'm listening to, rather than being just a witness to sound...just be ready to shop around for mods or different pads if you find them uncomfortable at first.