It has changed quite a lot, beyond the tracks & cars that were added.
Besides tweaks to Sport Mode and the additon of GT League, the biggest changes have been in the physics and tire model. The tire model is still woefully simple, but the dynamic model & physics have improved quite a bit. Road cars feel very good now (no longer ice skating). GT3 cars are more planted now, although some have some annoyingly OTT understeer. The FIA championships have a large playerbase and great matchmaking, as do the Dailies at times.
Make sure you have ABS on Default for Sport Mode. I would leave TC off, too, as it is rarely needed and wierdly implemented in GTS. ABS you could tone down to Weak (which to me seems like "off" in other sims) when racing against the AI, or maybe in Daily A/B where there is no tire wear.
Hope you have fun. For me personally the single player AI stuff doesn't do it, neither in GTS nor in Assetto nor PC2 nor whatever. Online is where this game excels. IMO.