I'm having to share this game with my roommate. Needless to say, he is at 92 stars. I am at 106 stars.

Well I have just started playing it, and since I am really busy at the moment I can't play as much as I want.
Anyways my impressions.
First of all, I was a bit bored during the introduction. It took a long time to start the game which was a bit sad.
Second: the graphics were very good, and better than the trailers. All the colors are beautiful, the Beehive level would probably be the galaxy I would like to live in if I had a choice.
Third: The worlds are not varied at all. I was disappointed with having to visit the same worlds with only slight variations for different missions. The different galaxies are cool, but they have a finite and really unsatisfying small amount of worlds.
Fourth: Controlling mario is excellent with the Wiimote. Collecting starbits while running around is soo cool.
Fifth : There are too many lives. I would rather there be no 1ups for collecting 50 star bits, and there only be 1ups for collecting 100 coins.
Sixth : This game does not feel like a chore for me, unlike metroid prime, so that is excellent.
Seventh : The music is excellent, sooo much nostalgic values.
Eighth : Gravity is very interesting, but less than I thought.
Ninth : Camera is very good too, no problems there.

I should say have around 17 stars in 3 hours or so, and right now am at the 2nd grand galaxy.
Overall I was not blown away as much as I had hoped, but the game is undeniably fun to play. About it being the best game of all time, hmmm I wouldn't agree. Super mario 3 would still be my favorite. Anyways, that’s what I think up till now.

I ordered my copy from amazon but it hasn't arrive yet.
I planned to give it as a gift for Christmas and now I am tempted to "test" it first, :D

Quick, someone say something bad about SMG so I don't HAVE TO open it.

I've got a star with over 100 coins. Like star bits, you get a 1-up for each 50 coins, but apart from that, nothing happens.

It was the ghost galaxy in the garden, if you're wondering where I did it. 

My wife picked up Galaxy for the family on her way home from work last Friday. We spent some time playing it Friday evening and again last night, and while I'm not 100% sold on whether or not this game should be supplanting OoT (or even Mario 64) at gamerankings, it's definitely up there in quality. First things first, the music is phenominal. The gameplay, the graphics, yada yada yada are all Ninty-standard quality -- I'd expect nothing less -- but the orchestrated score really makes this title stand out from everything else.

Now, the part I really wanted to comment on is the two player co-op, which some critics and players have complained about as "tacked on." I think it's brilliant.

Last night, my wife took a seat beside me to watch, so I tossed her a controller and asked her to help. She'd watched me play a little on Friday evening, so she correctly guessed that she could pick up star bits while I played. I mentioned to her that I'd read the second player could pin-down enemies too, which turned out to be a rousing success and a lot of fun for her. One particular incident that came up was during the second battle with Bowser Jr., where she found that she could hold the Magikoopas down in the path of a Bullet Bill, wiping both out, allowing me to concentrate on picking up Koopa shells and aligning myself properly with Bowser Jr's airship. It was quite hilarious. My wife was given an opportunity to help while not making the game too simple, and it turned out to be a lot of fun for both of us; maybe the most fun we've had together with the Wii since that first week we owned it and tore our elbows up playing Wii Sports tennis and bowling too much every day.

Galaxy is awesome, and the co-op is one of its defining features.

 How do you "hold down" an enemy with the 2nd player?  Is it an A+B thing?  I've shot bad guys, made mario jump, etc., but I've not "held down" a bad guy...

When 2P press the A button, there will be a small circle surround the cursor, then most minor enemies inside the circle will be freezed. Not all types of enemies are affected.

 Sounds like you have some pretty good impressions so far, but I will say you shouldn't solidify your opinion of the game until you get a chance to play some of the harder levels past 80 stars.  I had my mind made up after I beat it at around 75 and now I find myself thinking it is getting better and better past 80 stars as I go for the 120!

I don't know if everyone is like me and thoroughly enjoys genuinely tough levels but if you do I think the fun factor ramps up quickly towards the last 40 stars.  And I am looking forward to playing through again with Luigi as he will also make things more difficult =P 

 Yeah there is also a short recovery time for the enemies and a skilled second player can hold down 5 or 6 enemies at once.  If they are really skilled they can do that while still collecting star bits and doing other things as well =P