I watched this when it aired originally and loved it, which is hardly surprising given that I love wizards and magic. I recently had the chance to watch it again and it's still excellent.
Yes, the cars, the fashion and the skateboards all make this a very eighties show, but the storylines are still relevant and fun to watch. It wasn't just about the magic, it was about growing up, becoming your own person and about friendship. Growing up hasn't changed that much!
By today's standards it's probably a very tame show, but I like watching shows in which characters care for their friends. Yes, Zac and Leo fight sometimes but they're real friends and Mr. Merlin and Zac also really care about each other. It's completely different from, say, Gossip Girl in which friends are mostly backstabbers and you can't trust anyone.
If that makes Mr. Merlin an old-fashioned show, then so be it. I still love it.