I found the game very deep and rewarding even with just one license. With over 70 cars to choose from, there really is quite a variety in driving styles throughout the different models over the decades.
It almost goes without saying that the game controls impeccably and sounds great (this is Need for Speed, after all), so the excellent variety of play modes and fresh-feeling historically-oriented gameplay should be more than enough to convince you of the titles worth.
Unleashed's control is among the most frustrating of any racing game I've played in a long time. Maybe it's just the track layout, or maybe it's me, but I found my Porsche smacking straight into a wall or spinning out of control about every time I blinked.