Let me start by saying that I believe the tyre changes were absolutely necessary, tyre failures as Coultard described it are driver killers and had to be changed.
That said however, the change of the tyres mid season drastically affected the run of the championship. Red Bull have admitted that the tyre changes fell into their hands, and that the change to the new compounds allowed them to withdraw the maximum performance from their car.
There were obvious losers too, Force India and Ferrari moved back several places in terms of relative performance. Ferrari, who many have tipped as being the best all round car at the start of the season, is arguably the 4th or 5th fastest car now behind RB, Merc and Lotus - not that I believe the sum of Ferrari's miseries is all down to tyres but it seems to have played a big part.
What annoys me the most in this is that the teams got data on the tyres at the end of last year, and presumably used that data for car development. I strongly disliked that fundamental changes had to be taken in the middle of the season. Teams that did their homework, and developed a car to work the tyres best over the course of a race were penalised. They were penalised in terms on race performance, penalised in championship standings, and ultimate penalised in developmental costs and the amount of money they will be rewarded for next season if they drop places in the constructors.
The blame is often attributed to Pirelli, however Pirelli builds tyres to the specification that the FIA ask. The FIA not only asked Pirelli to build tyres that would degrade quickly to provide more entertaining races, but they also limited in and out of season testing which could have prevented such issue arising in the first place. Safety issues should have been ironed out before we had blow ups during the season, and the result of that was a fundamental change to the Formula in the middle of the season, with Pirelli acting as the fall guy.
Pirelli have a right to be angry, and their threats to leave F1 without more testing are justified.
I want to know what are the FIA doing about this? How will they prevent this in the future? How do they explain to teams who spent a large amount of money developing a car around tyres that would degrade quickly where their money went? How do they explain to them their lost positions in the constructors? How does this whole issue fit in with the drive to reduce costs? What does this mean for safety in the future? I think they have a lot to answer for, and pointing the finger of blame at Pirelli doesn't cut it.