Fast forward a couple years: Super Mario Galaxy 2.
I actually found this game to be a great improvement on the original (which was pretty good to start out with). The original game has 242 stars, but the second 120 stars are just repeats using Luigi instead of Mario, and the last two are just glorified cut scenes. Yes, I got all the stars. A couple weeks ago I got all the stars in Super Mario Galaxy 2 as well. However, the second 120 stars in that game are hidden in the levels and thus not as redundant as in the first game. Also, the last two stars come from a "Grand Challenge" galaxy that is easily the hardest level in the game.
Here's proof of all 242 stars in Super Mario Galaxy 2:
Full disclosure: I did not beat either Super Mario Galaxy game by myself. During both games I had my wife helping out as the second player. This helps immensely. I may have eventually been able to beat all the levels without her, but I more likely would have given up and moved on. During Super Mario Galaxy 2 I had my kids watching and helping too (that is actually helpful when we looked for the hidden green stars).