I haven't played F1 2010 yet, just haven't had time but I'm getting it anyway, but whilst I have been (and trying to remain) open minded and a bit optimistic about it, I haven't once considered that it would replace GP4 for me.
There's so much time and effort gone into making GP4 what it is, and if you set your game up correctly, with good mods, and get it accurate, then it's hard for anything to touch it, in my opinion.
I was a little bit "concerned" that F1 2010 would start a decline for GP4, but never really thought that it would spell any kind of doom for GP4, because the purists amongst us were never going to really ditch GP4 for F1 2010, I don't think....??
You can see though that developers these days have to put so much effort into making a game look nice for it to be contemporary and keeping up with the standard, that some fundamental things get overlooked.
I think the attention to detail in GP4 as a simulation, it's accuracy over a 100% race etc is just fantastic. And whilst F1 2010 looks stunning, it only adds testament to what a fantastic game GP4 is. Let us not forget it is 10 years old too.
I am so glad that GP4 is still the benchmark - at least as far as I am concerned. What a legend of a game. BUT it wouldn't be what it is without the amazing community and the countless hours that people have put into improving it, because it had its fair share of faults "out of box" too.
Long live GP4