The first time I played this game on the Wii, it took some time for it to grow on me. I remember enjoying the game and thinking overall it was good. But I also remember thinking parts of the game were quite weird. I'm glad Nintendo included the game in its 3D All-Stars package to play again. In the past couple of years, I have played every major Mario game on the 3DS or Switch, going back to the NES days. Super Mario Galaxy is on the podium in terms of best Mario games, and might be the best Mario game ever made.
To a large extent, comparing games in a great series like Mario is pointless. There are so many good games that span such a long timeframe, it is really impossible to rank them fairly. This is especially true when comparing games across multiple console generations. With this being said, let's start with the 3D era of Mario games, which starts with Mario 64 and goes to the most recent game, Odyssey on the Switch. Galaxy is the best Mario game in the 3D era. Let me explain why.
Galaxy is basically a better version of 64. It's essentially the same game. First the negatives. Parts of the game are quite odd, like the plot (beyond Bowser taking Peach). Accessing stages through the space station works OK but is not as original as jumping through the paintings in the castle in 64. Since the game originally came out on the Wii, you have the sometimes awkward motion controls to deal with as well. These are all very minor negatives. You can ignore the plot and Rosalina's weird story telling. The motion controls, at times are a hinderance, but at other times, like when collecting star bits, they are beneficial. The negatives in this game are very, very minor.
Galaxy has the best level design of any Mario game. They are beautiful to look at, intuitive, original, and fun. I rarely had to use a strategy guide to get a star. The levels naturally flowed, leading you to the star. This is different from the levels in 64, where often times I wasn't sure what I was supposed to be doing. The camera and control issues that plagued 64 are gone. Occasionally Mario would run in circles when trying to go straight, but otherwise the controls and camera are markedly improved in this game. This improvement is in spite of the fact that a complex physics model is present, with gravitational forces pulling Mario in different directions as he progresses through a stage. At times, this would induce dizziness, but generally speaking it was fine and added to the uniqueness of the game.
Comparing levels between Galaxy and 64 is a good reason why comparing games across console generations isn't fair. In the 10+ years between the release of 64 and Galaxy, obviously a lot of advancement took place in terms of what gaming consoles could pull off. Mario 64 was amazing at the time, and parts of it remain amazing today. Galaxy, however, does everything 64 does, but better.
Galaxy not only has the best music of any Mario game, it has some of the best music of any video game.
Let's briefly discuss the other games from the 3D era of Mario. We've already unfairly compared Galaxy to 64, so let's move on. I won't spend any time on Sunshine either, as I recently had a post about that game as part of the 3D All-Stars collection. Odyssey on the Switch was a fun game. My girls and I have played for about 90 hours, and we've collected nearly 500 moons. I don't think the game is as good as Galaxy, though. Except for the parts where the game transitions to 2D, which are fantastic, the game itself just isn't that memorable. I want to spend the most time talking about Galaxy 2. The game was somewhat strangely omitted from the 3D All-Stars collection. Therefore, I have not played that game since it originally came out on the Wii. While Galaxy 1 left a lasting impression on me that I remembered, I honestly don't remember much from Galaxy 2. My post from 2010 about Galaxy 2 said that it improved every aspect of Galaxy 1 and was a great game, so I will trust that it is a great game as well. For the purposes of ranking, I will include Galaxy 1 and 2 as a single entity on the podium.
For those who are curious, I have Super Mario Brothers 3 from the NES and Super Mario World from the SNES as the other two Mario games on my Mario podium. Despite being 30 years old, both games are a lot of fun to play, even by today's gaming standards. I will place those two games to the side of Galaxy, which in my opinion stands at the top of the Mario Bros. podium. What a fantastic game.