Even knowing that this is GT5 brand new engine developed, I'm sure GT6 would get better and probably not going to take as long. Knowing that lots of people is praising FM4 for their features, we don't know how the game is going to be turned out yet. There may be bugs who knows? Lots of people were hyped from this forum about GT5 and was very disappointed with FM3. Now it's the other way around with GT5. I think PD problems is the fact they were developing two titles which was GTPSP and GT5 at the same time.
In my personal opinion, I bought GT5 for it's graphics and physics. I was so curious to see how the ps3's capabilities can turn out, which is the best experience i've ever seen from a console.
I'm sure many of us seen from the gran-turismo website about what to expect from GT5. When GT5 was in development, I've seen lots of complaints from this forum about no reverse lights, realistic smoke, skid marks, day/night transition and weather. By seeing all these features into GT5 that shows that they are hearing us. Also people mentioned about livery editor as well. Kaz said he's not ready to implement that feature yet into GT5 (maybe GT6?). Even with this new update may have disappointed some of you but people were asking for the ability to wear different costumes from a-spec. They already implemented it. This shows that you can criticize a game for what you want. I think the best way to criticize for the things you expect from GT5 is to go onto Jordan's feedback section. But in my own guess, we may have a way better game for GT6 but there's still going to be criticism to make the game better wether the game is a success to many of you or not.