I'm not sure, I think Enthusia is great. The Enthusia Life mode is a bit w/e because of the point system and how easy it is to fuck it all up on a race. However I think the car selection is 10x better than GT4... because they actually get more special edition cars than normal cars.
The leveling up the tuning of your car system is whatever. I have my pros and cons but I like the fact that it's simple. Your cars charactherictics improve and you can tune anything you want just like in GT4, just no numbers. And they show you exatcly how much more oversteer and understeer you're getting.