My feeling is that is a very good businessman. He proved to be very good at finding rising stars of F1 (Michael, Alonso).
On the other side, I don't really like his way of managing. He puts himself in a monopole situation in renault, where he is the team manager and the drivers agent. How can he be objective and fair in this situation ?
We clearly saw him firing Trulli just because Jarno didn't want to extend his contract with him.
I also hated the way he fired him, finding ridiculous excuses like the French GP. Jarno lost 2pts there (beeing overtaken by Rubens in the last corner). What about Alonso who lost 5 or 6 points in Monza when he went off track, trying to resist to Button ? What about Alonso losing 8 pts in Monaco, crashing himself as he just could not follow Trulli ? Nothing, and that's not Fair.
If you looks at Renault's drivers policy over the last years, you can see that Flavio just did the things that would bring him the much money. He fired Fisichella who was better than Button in 2001 and engaged Trulli, then Fired Button who had beaten Jarno in 2002, in order to engage Alonso, then fired Trulli who was faster than Alonso in 2004.......what about next year ?
When everything's fine, FB is surely very cool and nice with everybody, but when things start to be hard, he seems to be a different person. The kind of person that flames you, then realize that there is a camera, so show off his great smile, puts you in his arms like a good old friend. Some kind of hypocrit in my opinion.