Yay! Heat in the winter is good!
It's a lot of work. I replaced a gas furnace earlier in the year. Other than lifting the old one out and lifting the new one in, it was just a lot of little tedious things that need to be done. However, I did enjoy fabricating a piece of ducting to connect the new furnace to the old duct. The biggest problem was getting the various parts. Home Depot (UPS sending ship to store) kept losing my packages and I'd have to re-order. Happened twice--never had an issue like that before.
Anyway, we have good heat now and hopefully a smaller heating bill (I put the money we saved by doing it myself into a super efficient model). <fingers crossed>