The years I followed F1 most passionately were the mid-90s until around 2010.
In this time, Mike Gascoyne worked for many different teams and seemed to be rated very highly by a lot of people.
But the results some of his cars achieved were less than convincing. His first proper Jordan (2000) wasn't reliable, Renault's real success came after Mike had gone, and Toyota never improved despite all the investment. Did he turn up any trees at Spyker/Force India and or Caterham? Not that I remember.
So how good was he really? Worth all the millions he was paid, or was he 'stealing a living' for many a year?
I'd be interested to hear people's thoughts about this. 
He joined Toyota in early 04, which they finished in 8th with 9 points, the following year with the car he oversaw they finished 4th with 88 points.
At the end of 05 after the 06 car was designed to run Michelins the head company switched to a Bridgestone contract because IIRC they were equipping their road cars with them. The tyres were a totally different concept to the Michelins and the car didn't work on them. I think this top down managerial interference is what led him to leave but that 1 season was their best result in F1.
Jordan in the first half of 98 had a reasonable but fragile car and hadn't scored a point in the first half of the season, in the second half after he joined they scored their first victory ( a 1-2) and racked up 34 points to finish 4th, the following year with Mikes first car they fought for the title (with help from McLaren and Ferrari's misfortunes) won 2 more races and came 3rd with 61 points. The 2000 car was fast but fragile again as Jordan overextended themselves trying to make their own gearboxes IIRC .
He joined Bennetton in 01 when they finished 7th with 10 points and 3 years later they were 4th on 88 points with their first victory (as Renault).
Caterham may have ended a disaster (after Gascoynes departure) but in the first 2 years under his direction they were by a country mile the most stable and respectable of all the 3 new starts.
The guy certainly had a reputation as an arsehole on a human level but he knew what he was doing technically and no team he joined ever went backwards barring that single Jordan season.
Curiously, if you look at Gascoyne, Newey and Chapman, they were all race winning designers and all quite tidy drivers in their own right, I always felt being a driver gave them an edge as designers over their peers.