I would say that the M50 is definitely not an overrated can. There are many headphones from UltraSone, Sennheiser, and other top brands which cost more but don't provide an equivalent sound quality. They are certainly the best "bang-for-buck" purchase you can make. I haven't heard a better headphone for the same price, anywhere.
However, the M50 IS a "wow" can, meaning that it makes your jaw drop the first time you listen if you're coming from consumer-grade headphones like Bose or *shudders* Monster. This 'wow' effect begins to wear off as you continue listening to them. It becomes less "fun" to listen to music over time, if you know what I'm saying. Other headphones, such as the DT1350, do the opposite. They don't jump out at you and wow you to begin with. Instead, they slowly reveal themselves to you and, over time, make you long for every chance to listen to them.
I can say that I have owned the M50s for quite some time, possibly 1-1.5 years now, and I listened to them almost exclusively for that time period. Now that I know them so well, I'm left longing for something better, or at least something different. It became boring.
By sheer luck, I happened to find an old vintage set of headphones on Etsy. I ordered them because they are a beautiful set of headphones. I expected them to sound terrible, so I thought they'd make me 'remember' how good the M50s were. They actually did the exact opposite. They turned out to be an extremely fun headphone, with an almost natural frequency response. I haven't listened to the M50s for anything but comparison since I got these headphones, and when I did listen to them, I realized that most negative claims about them were true.
In a sense, the M50s turned me into an audiophile. At first I thought they showed me everything I was missing. Then over time I realized that the M50s are just the tip of the iceberg. I spent $20 on an ancient AKG K-240 knockoff and now I like them more than the M50s.
So, if you want to become an audiophile, I'd say that the M50s are a great choice.