Shortly put, one of the games you can never know all about. Anyone who claims to do that is a bad liar. Also pretty addictive, especially online(after you've learned the AI and some basics).
Some claim the graphics to be dated, and some go for, well, illegal game modifications to "improve" way or another the various aspects of the game, usually mentioning graphics first. I dont think graphics are important in these kinds of games... But then again I also play Matrix strategy games. You know the ones where you play half a year to lose against AI. Il-2 is pretty similar, you can play for a year and still not learn the basics. Not that I have.
If you're going to get the game, practice the basics offline(takeoff, landing, set up some unarmed AI bombers to have some gunnery practice etc.) before jumping online. Online servers vary from "airquake" style games(you can jump on these practically right after install & updates), more difficult, usually objective based axis vs. allied ones(that you are likely leave shortly frustrated if you dont know the basics, at least) and campaigns. To keep playing fun but to keep learning and giving yourself new challenges, you might want to begin with the easiest ones and move to more difficult settings once you start feeling you might survive a sortie/get a kill or 2 on it.
