The maps will be about the same, the rest of the feature set is vastly different.
If you -need- to play videos on your dash then get the nav with ML. Otherwise it's massively not worth it.
Aftermarket systems will let you:
Get realtime traffic data
Get realtime movie/gas/weather info
Update maps for $75/year instead of $300
Fully use the device while the car is in motion (unlike the OEM that cripples itself while driving unless you hack it)
Play audiobooks, view pics, etc from flash memory in the unit
Move the unit to a rental car if traveling (or your wifes car if you have more than 1 vehicle you take trips with)
Save $2000-3000 on buying aftermarket instead of OEM
Improve the resale value of the car (nav is bad for resale)
Get a new unit with even MORE features the OEM can't do in a couple of years, again for thousands less
Custom update the map info using your desktop PC with custom routes, custom points of interest and destinations, etc...
You do lose the backup camera... but a few aftermarket nav units can do that too if you really feel like adding the feature, you'll just have to install the camera yourself. All the other OEM features (handfree bluetooth calling, phonebook integration, turn-by-turn directions, etc...) are available in the aftermarket for a lot cheaper, plus all the extra features the OEM can't do.
I mean no disresepect to the folks who paid thousands for their nav... and honestly if you bought an 06 or something the aftermarket choices weren't nearly as good as they are now (or as affordable) either... but nowadays it doesn't seem worth the cost and all the lost features to me though.
Do be sure and get a unit that'll fit in your console or glovebox (unless you plan to just take it with you) so you can keep it out of sight if parking in a questionable part of town... I highly recommend the Nuvis from Garmin (and I don't work for em
) and I highly recommend the Garmin friction mount, which fits perfectly in the flat area of the dash right above the center stack and avoids having to perma-mount anything at all.