I've always wanted to try this series but I don't have an Xbox..Blah
Looking forward to GT5 myself though, was really expecting a GT to come out with PS3's release kinda like PS2 and GT3, alas the prologue version doesn't cut it.
edit: Say it just occured to me, is there a good racing game for the PC similar to these two? I mean one with an extensive career mode, oodles of cars, preferably historical stuff, etc. I've tried the new need for speed shift, but quite frankly it's a let down. I don't know, I just don't like the feel of the steering and braking in that game. Also I don't really like the selection of cars either, plus the # it has is pretty puny in comparison to GT (dunno bout forza, never played it).
The best racing sim/arcade hybrid type game I've played for the PC is probably Test Drive: unlimited...Unfortunately it's pretty buggy on my computer, likes to freeze and crap, I think it doesn't like quad cores or something I dunno.