I've been using rf2 for quite a while now. About a year. I've raced some other sims before like iRacing. I will make it somewhat easy to find what you want:
Graphics
This is the main thing people don't like about rf2. It's not as good as other sims. This doesn't mean it's bad. Everything in rf2 has one big goal: being straight forward. The graphics are no exception. The new post processing already makes it look way better though and the rain effects are great. Recently they updated rf2 for better performance. This really helps.
UI
The UI is straight forward. Not as good as other sims but it's not as important to rf2 users. They are quite close to release the new UI. This one is based on Chromium. This means you can basically use HTML and CSS to make your own UI.
HUD
The rf2 HUD's are good but also not as good as other sims. Again it's straight forward. They released their new HUD recently. This one is way better and optimized for higher resolutions.
PHYSICS
The tyre physics are the best. There are no sims that can tip to the rf2 tire model. The tire flex is insane. You can also see it in replays and it's unbelievably detailed. They cut open a few tires to replicate it and it's really good. The chassis flex is also insanely detailed. It really affects the car and it makes for a great experience. Rf2 is a real sim (my defenition of sim). It's straight forward but at the same time detailed as ****.
FFB
The ffb is good in rf2. Most people have problems with it because it's to raw. The others sims are way to smooth most of the times. This ffb is awesome but you need the right wheel. It works great on Direct Drive Wheels. Also pretty good on brushless motors. Not really good on geared wheels (like logitech). I have a Logitech so it (maybe) doesn't feel as good as other wheels on the market but it's enough information to be fast and have fun.
AI
To start: The rf2 AI is great when using the correct settings for a car/track combo. I don't race them that often because I like online racing. You can have quite good races on rf2 with the AI. It's practice and error though. You need to try out settings.
The sound in rf2 is good but can be improved. Heavily depends on the car that you are using.
So, rf2 is a great sim and a must own to me. Not only because of the sim itself but also the community. The Discord server is great and actually the server I use most of the time. It paves the road between the developers and the users. It's awesome. Rf2 is a great sim but you need to put a lot of time into setting it up correctly for your situation. Normally this would take ages. Luckily you can use the
Discord server to get your information. I would also buy it because Studio397 is doing some interesting things to the sim. I'm always hyped about upcoming stuff. If you don't buy it now you will probably buy it in the future. It's being improved really fast. The new content coming is great (like sebring, lmp3 cars, some historic cars). You should check out the
roadmaps. There you can see what rf2 is all about and what is being worked on. Coming from iRacing I like the leagues but that's personal preference. The modding community is great but the mods can be low quality. For this you need to look around and ask what mod is good quality. For V8 supercars for example you have the RSM Mod. You can look around in the
Steam Workshop. Most mods are reasonable quality there.