Since when does having one melody make the theme bad? Most of ZUN's themes are like this, and yet most of them are exceptionally good.
Most? I don't know; maybe. But a decent amount of his music has more going on than most of his extra-stage themes, which is why I said what I did. Not that those are the only places where he beats a melody into the ground, but they're good examples.
Zil - I don't hear it. The occasional change in pace, key, and instrumentation (and the obligatory keyboard run), sure, but that doesn't do it for me. The melody remains essentially untouched. I'd find the themes more interesting if their lengths were halved; sure, it'd play twice over the stage, but there'd be far more new variance and it'd remain far more engaging. Other vgm, like old Mega Man tracks, were often exceedingly short, but they were so packed with ideas that you could loop them many times without getting bored. I can't think of any ZUNmusic that I dislike at the beginning (even with the intolerable auto-vibrato of ZUNpets), but I can think of many pieces that I can't stand after a minute and a half.
Good thing we have ~opinions~.
Sounding a little snippy there. I thought my tongue-in-cheek parenthetical would have been enough of a tip-off that I wasn't trying to hurt feelings. Regardless, most of the ex-themes are repetitious, and I dislike them and had disagreed with your earlier assessment for that reason. I didn't think I needed to preface what I was writing with the disclaimer that music appreciation is largely subjective.