I have used redline on-and-off since not long after its release. Its a great racing game at a great price.
My only gripe is about the online multi-player environment. It is a great concept, but has an achilles heel. One of redlines strengths is the capacity to build and use custom tracks and custom cars. Unfortunately, in the multi-player section, it is one of redlines weaknesses. There are so many custom cars and custom tracks that trying to find someone running a race with tracks and cars that you have is almost impossible. You cant race on someone else's server unless you have all the cars running in the race and the track they have chosen. I think that this is one reason why the multi-player part of redline has been a bit of a ghost town over the last year, certainly compared to what it used to be.
A solution, at least for the missing cars, may be to somehow make the cars physics specs available to all players who dont have the cars plugin, which are then applied to some generic car included within redline. It mightnt look as pretty as the hotted up "real thing", but at least it might make the game accessible to those without the cars plugin. I know you can download most cars and tracks, but this can be annoying if you have to do it every time you want to race someone online. Another alternative may be to have some type of p2p software built-in to redline that enabled direct download of track and car plugins between player.
Anyway, just my two bobs worth.

Brad.