Maybe Luke Perry is getting out of "Beverly Hills, 90210" while the getting is good.

Yes, indeed, ladies and gentlemen, Perry bows out of television's most famous ZIP code in tonight's episode (7 p.m., Ch. 13). And his departure is sort of symptomatic of what's wrong with the show these days.Perry's character, Dylan McKay, gets married to Toni - the daughter of the man who had Dylan's father killed. And there's some gunfire and somebody dies.

(I won't give away the details, but regular viewers shouldn't be surprised when they're not surprised by anything that happens.)

But for all these fireworks, the episode will leave all but the most die-hard fans underwhelmed. When it's all over, it's less "Big deal" than "Who cares?"

And this for the departure of what was once the hottest character on one of television's hottest shows.

Almost all long-running television series have a natural lifespan. Normally, they take some time to build, they hit their peak (where they stay for varying amounts of time), and then they go into decline. Some decline faster and farther than others.

Well, "Beverly Hills, 90210" is waaaaay past its peak. A case could easily be made that - creatively, at least - the show has been on a downhill slide since the regulars graduated from high school 21/2 seasons ago.

You know you're in trouble when you have to bring in fresh male characters because your leading female character - Kelli Taylor (Jennie Garth) - has had sexual relationships with every guy in sight.

This show was never great art, but it used to be pretty good soap opera. It tended to get preachy at times, but it did actually deal with some serious issues.

These days, it's just pretty much dumb and redundant. It takes itself far too seriously to be good camp - like "Melrose Place," when that show is working right.

But it's too ridiculous for the viewers to take seriously.

It's not like anyone expects a great future for Perry in films. (Does anyone remember "Buffy the Vampire Slayer" or "8 Seconds?")

However, this would seem like a pretty good time to bail on "90210."

TV TRIVIA TIME: Contrary to some reports, Luke Perry was not in the original cast of "Beverly Hills, 90210."

He did not appear in the pilot, but joined the cast in the show's second episode back in 1990.

DEATH ON "SEAQUEST": In an apparent attempt to boost the ratings, "seaQuest DSV" (7 p.m., Ch. 5) is going to kill off one of its regular characters tonight.

Which would seem sort of odd, were it not for the fact that this mediocre-to-awful sci-fi series can use any help that it can get.

(Even your local television editor might tune in if he could be guaranteed that at least one character would die each week until "seaQuest" just went away altogether.)

I won't give away the secret about who's going to bite the dust. But then, judging by the ratings, most of you don't care anyway.

GOOD NEWS: For those of you worrying about whether the locally produced CBS series "Touched by an Angel" was going to be around for a while - stop worrying.

The show isn't a huge hit, but it is building. This past Saturday, "Angel" had its highest rating ever (an 11.4 rating and a 19 share) and won its Saturday 8-9 p.m. time slot.

"Touched by an Angel's" demographics aren't ideal - it skews older than the advertisers like - but CBS has so many problems in so many time slots that it's not going to mess with this one in the foreseeable future.