Well, it helps if you enjoy teen dramas. I watch a lot of them, so that aspect never bothered me. I think the show was partially popular at the time because there weren't really a whole lot of other superhero shows on at the time, unless you count shows that were already off the air like Lois and Clark or shows that weren't based on comic books like Heroes. Some of the characters the show introduced, like Aquaman or Green Arrow, had never before appeared in live-action, so that part of the show was an novelty at the time. Furthermore, the special effects, though probably dated now, were also better than what had been done before on previous Superman shows.
As for the characters on the show, Michael Rosenbaum's Lex Luthor was really superb. The teetering between good and evil for his character was fun to watch, as were his relationships with both Clark and his father Lionel Luthor. A friendship between Superman and Lex Luthor had never before been explored in great detail, and in most Superman stories, it was altogether unheard of, so it was a unique spin on the story.
Lois Lane was also really well done on the show. In my opinion, Erica Durance is easily among the best versions of that character, hitting on all of the aspects of Lois that I enjoy. She was funny, tough, and witty, not to mention very beautiful. I think she is very close to Teri Hatcher's version of the character in a lot of ways, though they obviously do have their differences and are not carbon copies of each other.
The show had a few very memorable villains throughout it's run. Lionel Luthor comes to mind immediately as being pretty deliciously evil, though some of my other favorites include Lex, Brainiac, Zod, and Tess Mercer. These are obviously just personal opinions, but I found those characters to be the best written, to have the best performances from the actors, and to be the most interesting of Clark's enemies.
It's not a perfect show, but I do find it to be highly enjoyable. If you're not digging it, maybe it's just not your cup of tea or maybe some of the original appeal is no longer as big of a deal as it was at the time the show was airing. Either way, maybe this will give you some perspective as to why it was popular or why fans love it.
