I agree it probably is (one of) the next-steps in the "progression" line. I do not wish to sound patronising to those who stay on M2k, because as I have said before - it's not what you have, it's how you use it. I am not saying that any tunes made on M2k will be crap compared to FL, but I think it is the next step up because, as JohnP says, it is more reliable, more user friendly, and there is just simply more to do on it. More things at your fingertips to play with, more opportunities for sound production, more variety - it is more flexible
But still, it's easy to get the hang of · it can look pretty and colourful as M2k does (especially as you can apply your own background) whereas some production programs can look dull · it can function as easily or as complex as you want it to. You can choose to just use samples, or you can explore the effects, synths etc.