Singling out mods is really bad business. We all know PnG which is a masterpiece, but again and again I encounter amazing pieces of work in GTR2. People spend countless of hours researching and working with the goal of accurately preserving motorsport history and accurately recreating motorsport events. Sadly, some of that amazing work is gone with nogrip down... and probably even more will be gone with GTR2 slowly becoming a history. That said, several mods that I spend the most time in. It really means nothing but that I spend most time in them, we all like different things
* DTM 2018 updated from
http://www.koelschbierbude.de. If you use those cars, make sure to buy URD T5 cars if even you never fire up AC. Those guys deserive magnitudes of order more than they ask for their work. I generally think that user must own all the games he/she uses models from.
* EEC 2.3 from
https://esport-racing.de/. There's fantastic pack for ADAC and BES and matching trackpack. Gives a cohesive Championship feel. Great looks, sounds and nearly perfect physics (subjectively of course). And you can simulate bigger events with those cars - 57 cars load fine.
* FRM TC cars - another huge work from
https://furinkazen.***********/furiracemods/frm-touring-cars with matching BTCC trackpack. Surprisingly good AI, and I hear they work on an update to use GTR2 damage model to the fullest.
* F1 1994 and matching trackpack from RD - one of the most polished paddle era open wheeler mod I encountered in GTR2 so far.
For those seeking even deeper simulation, Crew Chief GTR2 Enhancements plugin brings above mods couple of steps forward via adding more correct shifting, flat spots, dirt pickup, more rules and some eye candies like backfires/wipers. And, there's WIP to add DRS to the above DTM cars.
PS: yep, I agree with Shovas, VLM Sebring _is something_, can't believe how good GTR2 can look.