I have a 2013 car with the Tom Tom system and find it alright, although having been used to using Google Maps on a smart phone find it a bit of a step down from that.
However, in terms of maps i have always preferred Navtech over Tom Tom, as Navtech actually send cars to drive the roads like Google do and map them that way, whereas Tom Tom just essentially use an OS map. That means you end up with a lot more accuracy when it comes to one way streets and not taking you down gravel roads with Navtech than you do with TomTom and also finding TomTom thinks there is junctions where there isnt one, IE it is telling you to turn right but the road bends that way anyway...
Still getting along ok with the TomTom, and love the rest of the car!