1. Growing up I was always more of a Superman fan than a Batman fan, so I didn't really encounter a lot of Aparo's early Batman art (on B&B or BatO), although I understand that for many Batman folk Aparo holds a similar place of reverence that Curt Swan holds for we Superman fans. Aparo always struck me as a true professional, some to whom an editor could hand a script and be assured that 3 weeks later he would have the story done, to the writer's specifications, and it would look good. Never flashy, but solid. I also recall reading some of the Aquaman stories he had done (I think in the DC Digests) and finding those pleasing to look at.
2. When I did encounter Aparo's work, I had various reactions depending on where I was in my comics reading growth stage. As a kid, I appreciated his clean lines and solid storytelling (even though I would never have been able to identify it as such). As I got older, it began to look old fashioned and stiff. But as my tastes matured even further, I could once again appreciate the same qualities in Aparo's art as I saw when I was younger. Whet helped most, I think, was seeing Aparo teamed with the inks of Bill Sienkiewicz (on the Batman: GCPD mini-series); by taking away the smooth line inherent in Aparo's art and making it more gritty, I was forced to realize what a strong storyteller he was and appreciate the level of his craft.
(covers for Batman: GCPD #1-3 by Jim Aparo & Bill Sienkiewicz courtesy of the GCD. Click on images for larger versions.)