The first thing I would look at is your source quality. A lot of people don't realize that higher quality headphones will bring out the best and the worst in tracks.
While I wouldn't go so far as saying that Sennheiser doesn't ever produce lemons, their quality control is pretty high to my knowledge.
Can you give us some information about your setup?
file types, bitrates, soundcard, cellphone, amp if you're running one
Also keep in mind that, generally, higher end audio does tend to tailor towards a more balanced sound, whereas mainstream audio tends to overemphasize bass frequencies at the cost of higher frequencies
This may be why you feel the headphones are a little flat... for most headphones burn-in does play a significant role in opening up bass punch.