My furnace installation was acceptable, but there were certain things that I was not pleased with. First of all, the estimator said that the exhaust pipe couldn't be placed under some windows on the 2nd floor. The installers placed the pipe directly under these windows, saying "it was good enough". Also I discovered after they left that the furnace wasn't aligned properly with the walls and other things in the furnace room (it's visibly crooked). It would only have taken a few seconds with a tape measure to align it properly. I got the impression the install team just wanted to get the job done as quickly as possible, without regard to quality or craftsmanship.
To give them credit, they did replace a gas line to the hot water tank, which they didn't have to do. And I do love the new furnace.