In essence, it's exactly the same as what DSA has - get a train to a station, and wait for a bus. East Mids Parkway will have 1 train per hour from Sheffield, Doncaster station has about 6 or so. The buses from EMP to EMA are every half an hour and take 15 minutes - buses from Doncaster Interchange (attached to the station) are about every 15 minutes and take about 20-25 minutes. If anything, if the sole reason for choosing an airport was based on rail links, I (still) think DSA wins hands down (out of DSA and EMA, rather than all airports!).
Still, for EMA, I still think it's far quicker (and cheaper) to get off at Derby (from the North) or Loughborough (South) and get the Skylink, as what was originally there before. I understand East Midlands Parkway station was intended first to be a "park and ride" to London, Nottingham etc. and as an airport station second.