I have been sim racing for about 6 months now and have tried many sims including iRacing, rFactor and Game Stock Car, as well as many simcade titles as well. I can say without a doubt that Assetto Corsa feels like the best. That's not to say the others are without merit, they have their own strengths and weaknesses. But when it comes to communicating the way the car feels to you through a force feedback wheel, AC is second to none. You can truly feel when your car is riding on the edge of available grip and the car will react accordingly to the inputs you give it. The physics and FFB are something that need to be felt to be believed.
The AI needs some work but can be passable, however I feel that online leagues where this game will shine for those looking for strong, clean, competitibe racing. Public lobbies can be ok, however you may find griefers driving the wrong way and trying to wreck others. Ask around forums or check steam groups if you are looking for clean racers.
I hesitate to speak too much on controllers as I use a wheel and pedals, but I will say with many aids turned on it's not impossible to keep yourself on track. It may be a fine way to learn the tracks while waiting to purcahse a wheel.
I have no doubt Kunos will continue to supply top-notch free and paid content in the coming years which will be finely supplimented by content created by modders. AC will definitely be a hub for great racing from many different fandoms in the motorsports world. I highly recomend it.