Many...most...of the add-on trax, so far, are pants. The big ones (Nurby,
Le Mans) are out in multiple vers, each worse than the last. The best
venues are the little club trax, particularly those done by IDT (Independent
Developer Team): Falkenberg (a gem), Norisring (ditto), North Point (from
SCGT), Chatham (ditto), Metro (converted by somebody else), and Scotland's
wee Knockhill (a 3rd-party original).
Virtually all the trax now avail are conversions, most from F1C, some from
SCGT, some from Toca. Among the ones I like: Austria's A1-Ring (not the
Oesterreichring), Assen, Road America, Dijon (a wicked little track),
Phillip Island (Aussie V8 Supercars!), and the full Indy oval (quite a setup
challenge!).
There are a slew of conversions and original tracks in the pipeline, but
most modders are waiting for the international release...which has yet to be
announced (hopefully by this summer).
There are no new cars (we're all praying for the BMW M3 V8, Aston Martin
GTR, McLaren F1 3-seater, etc., but no word yet), but there are a ton of new
skins for the dozen or so cars that shipped with the game.
The homely little Lotus Elise is great fun to blast around the short and/or
city trax (Monaco, Knockhill) online, and somebody is working on a mod that
re-skins 25 of the little ***s for club racing. There is already such a
HFR racing:
http://www.racesimcentral.net/
You'd better speak French....