Without a doubt, Yoshi's Island is a fun stage to play in Brawl. Yoshi's Island is a great stage with great catchy music, cute art style and most importantly, fair to play on.
The best moments I had with Yoshi's Island, is the animation and music. The music while not the best in Brawl, is catchy and has a soft beat the fits the style of the Yoshi spin off video games and the stage well. The art style animation in Yoshi's Island is also enjoyable. The art style is neatly well done for Yoshi's Island with cute animations such as crayon based flowers that pop up on the stage. The changing seasons that happen in Yoshi's Island such as winter and summer, are also neatly done well that fit the style of the Yoshi games well.
Like Lylat Cruise, Yoshi's Island is a fun stage to play on for newcomers and veterans to the series. You do not have to worry about any cheap gameplay elements getting in the way as you battle your opponents on Yoshi's Island.
If there is a negative to say about gameplay action in Yoshi's Island, is that Yoshi's Island is a fairly small stage to fight on. The stage could of been slightly bigger to fight your opponents on like Lylat Cruise but overall, Yoshi's Island is a fun stage to play on Brawl.
Even if the cute based animation in Yoshi's Island does not appeal to you for a stage idea in Brawl and turns you off, you should still give it a try. Overall, fun stage to play in for Brawl.