I have no problems whatsoever with Delrin covers. Delrin is probably the most successful cover material in slipjoint history. I'd even bet that more knives have been produced with Delrin covers than all other materials combined. With that said, I do prefer Micarta when it comes to synthetic handle materials. Delrin gets to looking pretty bad when a knife is heavily used/abused, and can't be refinished easily like Micarta.
Some Delrin covers are far better than others though. The Case look isn't bad. Nothing truly inspired, but since they've used a number of vendors over the years, to produced their knives, the Case look is easy to replicate for the sake of brand identity.
Here's my only Case jigged brown Delrin, done by Camillus.
But Camillus produced much nicer jigged Delrin, IMHO. Some of their stag bone is simply marvelous.
I do LOVE Case's smooth yellow Delrin. Yellow Delrin is classic in a way that no other Delrin seems to be able to achieve. And Case gets the coloring just right.