Ive had a couple that were a little too sweet and thus unbalanced, but you're right, they tend to be almost dangerously too drinkable. But of course, with only 5.5% alcohol, they aren't at all dangerous!
But I think the corollary of this is also true: while it's hard to find an objectionable moscato d'asti, it's also hard to find a spectacular one. As you say, though, it's not a 'serious' wine (whatever than means), just a highly enjoyable one. Seriously enjoyable, I guess!
Is there a yummier summertime aperatif? I think not!! A few bubbles, gobs of fruit, some residual sugar and low alcohol - what's not to love?