The obvious question scouts and, subsequently, GMs had was with his skating. Having seen him play several games at the Under-18s last spring, and then witnessing him in person at the Habs rookie camp, there is no doubt that his skating has improved. Guillaume trained daily during the offseason on his skating, including taking power skating lessons, he's obviously committed to improving.
His skating looked fine against players three and four years older, it's quite obvious that he will be a dominant force in the QMJHL this season. I wouldn't be surprised if he hits the 50-goal mark this season and cracks 100 points, despite missing several junior games while competing in the WJC. Based on his play thus far this summer (top scorer at WJ camp, 8 points in three Q exhibition matches, dominance at Ottawa rookie camp), he's a favourite to make the junior team.
Latendresse has become very tough to knock off the puck, better utilizing his leg strength to attain position. He could always hit, and with better speed the hits are even more effective. He absolutely crunched a couple of Leaf prospects two years his senior, and against the Canes big Brett Carson was knocked senseless by a Latendresse crunch.
It's too soon to say he was a steal, but I'd certainly say the early returns are positive. His technique seems fine, he's plenty fast once he gets going; all he needs is a quicker first step and he'll be fine. The rest of his game for his age group is well above average.
Rated 65th means he should have been taken around 90th overall, with goalies and Euros in there, so I'm just wishing the Habs had waited until the 3rd round or so to take him instead of spending so much to get him so high. 
