After having a membership for 2 weeks now, I have got many impressions. Like mentioned earlier, this is not a game like GT5 where you can turn it on, run a race for 5 min than quit, iRacing takes much longer time than so. My experience with online racing is that other players have much better racecraft than any other game I have played. I like how people pass you in realistic places and don't just bump into you in the first corner. The game was also very easy to start up, didn't need to download many patches and manually install them.
So far I am enjoying the game, but I find it hard to invest so much time as work is very busy this time of the year. Will invest some serious hours of gameplay in the holidays.