Notice how it's better appreciated after Mario Galaxy came out...
Although I think that squirting gastric juice out of Yoshi's guts seems gross, Nintendo had to find a way of letting the player squirt water while riding Yoshi.
In all, this game's technical specifications (gaphics, sound etc.) are awesome, it's gameplay is engaging, although the parts where dark Mario steals your water pack and you have to run around blocks in space seems tedious. In conclusion, this game is worth spending money on, even if it wasn't on sale for only $19.99.