OK.
I'd say:
Exotic/Tuner/Muscle division is absolutely stupid. There should only be lots of classes (like, 350Z is roughly as fast as a Cayman, not faster or better handling) divided by horsepower or acceleration. Tuning would make them into another class. That solves everything, an ultra-tuned Supra vs a sports car like an F430 or Gallardo. A tuned 911 Turbo (like Techart GT Street) vs an older supercar - like an F1, XJ220 or CLK-GTR. New supercars can only race other supercars.
And one more thing: there should be always proof for existence (or, indeed, possibility) of a car similar to some that you may see in the game - if there is a some monstrous Civic outrunning an Enzo, show me it, and then you can put it in-game! If someone has put a huge bodykit on a 911 Turbo (TechArt GT Street) make it similar (or licensed) in the game. If someone offers a twin-turbo for a Golf R32, put it in-game. If someone could put an R8 engine on an A3, make it swappable.
But show it's possible!
And the tuning thing - I meant you get to tune cars (u dont drive them then) from each manner and tune them as you like. If you leave them stock or merely change rims, the game will make similar modest mods, if u rice them up, the opponents will be too.
Also I liked about HP2 the chilled racing - GT, Grand Touring, you felt covering long comfy and fastly travelled distances... It would be good if cars like Panamera or Rapide were there with a higher Ride Smoothness (Top Speed, Handling, Acceleration, Comfort - factors deciding about success in various situations)
There are factors that (in my opinion) make NFS crap - I'll try and list them for ya, though I'm sure u know them:
1. Ricing beautiful cars - bodykits look good on a Supra or Skyline, but a randomly generated Murcielago makes me sick
2. Random and anonymous opponents - who doesn't remember the Dylan dude, along with Parise from Porsche? Or Gotcha and Leadfoot of NFS3&4? Who however does, some random guys with randomly made cars (in U1 u could recognize them and names and rides) which are rice?
3. Only street tracks, teleporting to Mediterranean or some desert or wherever is not a bad idea keeping the city - cos ONE american city's rural areas won't give the variety of nice things you can see in Europe, USA and beyond (Australia? Africa?) - some imagination!
4. Learning it takes a Golf to smoke a Carrera GT
5. Pimpmyridehooomieboooy(TM) and Youdonthaveenoughreptoracemeyoupunk(TM) stuff - everything must be based on violence and street cred! (of course that sells best)
No nice and rich atmosphere (8 or 6 rich-ass people meet up in an exotic location and race!), just RESPECT counts...
6. Storylines trying too hard sometimes (a nice addition in U1 or MW, but U2, Carbon and UC are OTT)
7. Unrealistic things with the cops (destroying 30 corvettes a minute and going through roadblocks all the time) - again, show me how an old '98 Camaro smashes through a Crown Vic and keeps same shape (it may have stiffened chassis, rollcage and stuff) at least once. Cops in HP or HP2 weren't realistic but were more believable (no, don't remind me the helicopter), if they darn have so much money for Corvettes why dont they just get a tank and some SWAT trucks and block you properly, then bust you?
8. Little variety of things you can do (Where's be the cop offline?)
9. Stupidly easy opponents; in U1 they were aggressive and have shown desire to actually win the race.
10. Failures to include the two worlds together.
OK, now: how can you combine?
1. Make a city (Tri-City, Rockport, Bayview, City of U1, Palmont work)
2. Along with it, make other tracks to which you TELEPORT while going for the race
3. Restrict tuning to licensed and existing parts which are AVAILABLE FOR THE MODEL, but if there is a horrible rice thing available for an F430 it can be there
4. Make things that people liked about all the series - tournaments, outruns, reasonable cops, extensive tuning of the tuner type cars, reasonable Autosculpt, exotic locations and the city
5. Make a light storyline which isn't about crime syndicates - like, start as a tuner and get into exotic muscle world, start as a rich exotic fan and slightly appreciating tuner cars, being a muscly muscle fan and seeing what Imports have to give...
6. and most important... listen to what FANS have to say!