I think if you're a real petrol head Forza 3 still holds the crown. It's the closest thing there is to the real thing (debatable, maybe). Same applies to GT5, if you ignore the snot worthy controller support.
If you're comparing the TD series to either of these games, you're off to a sour start before you even completed the first licence. TD is basically just a bit of fun, and the more you progress the more fun there is to be had.
The reason there aren't many reviews yet is because the game is very much focused around it's MP factor, and to review it before there are any real number of people playing it would be unfair.
Yes, the handling is diabolical - I wouldn't even call it arcade. At least with arcade there is the whiff of an attempt to mimic real life. However, other aspects of the game excel hugely. In the first sequence with the California, the engine and the noise on up-shift instantly reminded me of when I drove the car last year. All of the cars sound just like their real life counterparts - and the same can be said visually
A lot of people in this thread seem to think the graphics really aren't up to much, which I cannot understand for the life of me - they look amazing! Especially the environments and weather effects, which help the game to give of a proper sense of 'driving'. Something which a lot of games fail to capture (GT5 in particular)
I don't think I'll ever pick up a driving game and play it to the same level that I did Forza 3. There is simply nothing which will come close to the geometry/realism which the game reeks of, but TD is still a great game IMO and those who don't appreciate it were probably expecting too much. What with the 5 or 6 years it took to develop GT5 (which is already catching dust on my shelf) it doesn't seem so shabby!