The lyrics, the droney music, the beautiful melody... I remember around Red when RC was talking about wanting to get into experimental song structures, and touted Angel as being the result... but Rosemary fit the bill 10 years prior.
Is there a studio Weezer demo? A RC demo? The recording we have is admittedly shitty, but the song is so gorgeous I find myself listening to it often. It's on par with the other material from the era, Prettiest Girl, Lover In The Snow... and I'd say in their own 98 way, all of these songs rival Blue/Pink.
Bring it back, boys. If you dare.
As a slight aside, I often thought Fun Time would have been an amazing single.