Pretty good deal, I think Calgary would have really been better off locking him into an 8 year deal though. Gaudreau is one of the best forwards in the league, and he's now scheduled to be a UFA in 6 years which is dangerous.
That said, I think $6.75M per is a pretty good price for the next 6 years, but I think if Calgary was honest with themselves, they would know that they won't be competing for a cup in the next 6 years anyway, and would be better off making sure they have Gaudreau for years 7 and 8 even if it means paying a little bit more now.
So I have mixed feelings overall about it, but I'm happy he won't miss any games this year from my fantasy pool's perspective!