Our extended family spent a week here in August. While we enjoyed our stay and would recommend the location to others, there were a few shortcomings which we will also cite.
Positives:
1) The house is large, modern, and provided ample space for those indoor days, and allowed each family to have some privacy
2) The beachfront is excellent. Nice and sandy, easy to walk out to the lake and enjoy a swim or play
3) The location offered a great deal of privacy. Not much traffic or noise
4) Enough lawn to have a small game of soccer or football
5) Amazing sunset and sunrise views, either from the dock or 1 of the 3 enclosed gazebos.
6) The owners were incredible to deal with. Very responsive and apologetic when issues arose.
Key shortcomings:
1) Water, water, water. While the lake was incredible, we did have 2 issues with house water during our stay. Day 1 the well ran dry, and despite effective recovery plans from the owners, I would not expect this to happen with a premium rental. We were less impressed with the Muskoka Rental company, who took a more laissez-faire attitude. And on our last day, the basement plumbing became clogged. Again, not the end of the world with multiple bathrooms to use, but a nuisance nonetheless.
2) The only other drawback is the lack of proximity to other activities or events (or even restaurants). MacTier is a small town with a Foodland and an LCBO. To do anything of note required a 25-minute + drive. Not a show-stopper, but just an FYI