The ATH-M50 has many reasons to like it and there are many reasons to suggest it to someone that is just getting into the hobby.
1. It is slightly bass heavy north of neutral. This is a good thing for someone entering the hobby because they often are coming from the mindset that more bass is better. God knows that I was concerned about the quality of the bass of a headphone when I first entered the hobby. Not only that, but I would argue that people in general like a sound that is a little bass heavy of neutral (see one of my favorite dynamic driver headphones, the HD650). Not only that, but people almost always want closed-back headphones when they first enter the hobby -- it's not until you start reaching audiophile territory that you really start desiring open-back headphones.
2. They measure very well and are comparable to significantly more expensive headphones strictly on measurements. Their waterfall CSD plots are incredibly clean for a closed back headphone in its price bracket. The implication is that the low-level detail retrieval of the ATH-M50 is better than I think a lot of people give it credit. If you're not sure how to read the plot, just do a little bit of research on the waterfall CSD plots and why it is more important than a frequency response graph.
3. The reviews on them are generally positive. Are there negative ATH-M50 reviews? Yes, but they're drowned out by the positive ones. Contrast that to headphones that I would consider as having mixed reviews, like the Ultrasone ED8 or the Grado SR series of headphones, which are typically more love it or hate it. The ATH-M50 is a safe suggestion in many cases.
4. They really don't require an amplifier. Most people that are entering the hobby want a headphone that is nice sounding to plug into their laptop or DAP. They don't want to carry around an amplifier because it is just extra luggage to carry around on the go. Once again, it's not until you start entering headphone audiophile territory that you start researching portable amps and start wanting one for your system. Most people don't want to carry around an extra thing just to amplify their headphones them they're on the go. You can run the numbers on the impedance and the sensitivity numbers on the ATH-M50 -- typical portable DAPs will be able to properly drive it.
Subjectively, and objectively, the ATH-M50 is a solid pick for its price bracket. If you go by the measurements, I'd argue that an equalized ATH-M50 punches significantly out of its price bracket as well. It's, of course, not universally liked, but there is no headphone that is universally liked. It's not the headphone to end all headphones, but it's pretty damn good.
