The driver I have found to be most disappointing is Mark Webber, he has struggled to beat McLaren and Ferrari let alone his own team mate. Webber should at least have backed up Vettel with numerous one-two finishes, and at least beat him occassionally rather than just once.
Massa has also been disappointing, he is getting the minimum expected results from his Ferrari which is usually 6th place. Sometimes he has fell below the minimum expectations of where he should finish. If both Massa and Webber continue there bad form throughout 2012, Ferrari and Red Bull should drop them for 2013.
Hamilton has also disappointed me, everytime he seems to come back from a bad run of form, he ends up returning to that previous form. He has had great race in China, Germany and South Korea, but it was painful to watch him in races like Monaco, Canada, Japan and India. Hopefully can rediscover his best form. I’d hate to see him leave F1 with just a single championship to his name.
I haven’t found anyone else that disappointing this year, everyone else seems to have met the level I believe they should be performing at. Drivers like Senna, Barrichello and Trulli haven’t been great either, but I didn’t expect them to perform well anyway.