I enjoyed the game mostly, but there were a lot of hard sections in it. I find SMB2j much easier than it but I have become quite familiar with its levels and now accept it as my Mario 2 so it's not a good comparison. What frustrated me was the fact that you needed a much higher percentage of Shines in order to get to Bowser. In SM64, you only needed like 70 stars or so out of 120. In Sunshine, you needed over 100 or something before the game even let you into the final area.
Getting to the last boss was most of the challenge at the end. Fighting the boss was more pathetic than jumping on Iggy three times in Super Mario World.
But I sure loved the majority of Super Mario Sunshine including its art and music.