*Disclaimer: Keep in mind that this is completely unofficial, it’s not made by Bigben Interactive, it’s entirely made by me. All that you in this post belongs to its respective authors*
TDU3 - Meeting other people
In TDU, when you drive on the island's roads you'll often bump into other players. When you meet other players, you can drive alongside them, chat with them, challenge them to an impromptu street race, or simply become friends. Sure, every other racing game nowadays lets you meet other people online, but TDU made every encounter seem special in some way. But if you're playing offline, there'll be AI racers roaming around the map, and you can race them too, in case you're bored.
TDU3 - Home, Sweet Home
Buying a house is fundamental in TDU, as you need space to store your collection of cars. In TDU2 you could even walk around your houses and customize them, a feature that no other racing game currently has. Owning many houses also gave you points. TDU is perhaps the only racing game where even buying a house feels somewhat special.
TDU3 - A new set of wheels!
When it comes to buying a new car, no game is as immersive as TDU. You can walk around the dealership, admire the cars in each of their little details, compare their stats, open the doors, start the engine, play the horn (don't do that in real life!), and even take them for a test drive (the game's title is Test Drive, in case you forgot)! And when you buy them, you get to chose the rims, the color of the body and the color of the interior, then the beautiful desk lady gives you the keys to your brand new car (or bike). No other racing game has all of that, not even Forza Horizon 4 and The Crew 2!
TDU3 - High speed racing!
In terms of variety, TDU is quite good, offering events such as time trials, street races, lap knockout and speedtraps, plus some extra missions such as delivering a car to a designated spot, or give a ride to a fine looking lady. As for the racing, considering how things are going in the Forza series, i think the game needs a system that rewards clean, correct driving and punishes dirty drivers, a bit like Driveclub. That way, there will be a lot less cheaters, and fun will be guaranteed for everyone! Win-win!
TDU3 - Offroad
TDU2 featured offroad racing, and so included vehicles such as the Lancia Delta Integrale, the Subaru Impreza, SUVs, etc... and i think the concept of offroad racing should be expanded in the next game. Considering Kylotonn Racing Games (TDU3's possible developer) has a lot of experience in rally racing i don't think this will be much of a problem.