Veteran Filippi made over 100 starts in the main series alone from 2006-2011, culminating with a runner-up finish in the standings last year.
The Italian is moving on to race in the IndyCar Series this season with Rahal Letterman Lanigan Racing, starting with the Indianapolis 500.
That means he won't get to experience a 12-round calendar that adds races in Malaysia, Bahrain and Singapore to the traditional European schedule, but Filippi says he is delighted to see GP2 expanding.
"It's a world championship now, and that is great," Filippi said. "The Asia Series was going down a little bit, and it is good that GP2 has one big season.
"It's going to be tough, and it will be an interesting season to follow. It is always hard to judge a season, but I am looking forward to watching it, even if I am not there anymore."
Filippi added that he expected the new rule forcing teams to use two tyre compounds over the race weekend to add to the interest in 2012.
"There is this extra question mark about the tyres now, with the double compound," he said. "It's going to be interesting.
"Will everybody need to start with the harder tyre because they are in traffic and the car is heavy? Then, when do you switch compound, and how big is the drop off?
"We will see great laptimes in qualifying as well because of the extra grip, which will be nice."
The five-time race winner has also tipped Lotus GP (ART) driver Esteban Gutierrez as one of the title favourites.
"Sometimes you think a season doesn't look as tough as the one before, but the young guys improve very quickly," he said. "It's quite likely to see a big step from one of the guys who was a rookie last season.
"Gutierrez didn't have a great season last year [one race win, 13th in the standings], but he has the skills and he is intelligent, so he will be strong."