Perhaps "artistic demise" is too strong a phrase, but something happened to Elton John in the mid-'70s.

The mercurial talent went from making mostly brilliant pop-rock to borderline hack work in, it seemed, a matter of weeks.He charted with the gorgeous ballad "Someone Saved My Life Tonight" in July 1975 and some three months after brought forth the insipid "Island Girl."

A few singles later, he reached new lows with "Don't Go Breaking My Heart," a duet with the amorphous Kiki Dee.

It's never been the same. Although John has enjoyed steady, sometimes spectacular commercial success since '75, his music has been largely flat. Stack "Nikita" against "Madman Across the Water"; "I Guess That's Why They Call it the Blues" vs. "Take Me to the Pilot." To these ears, there is no comparison.

After shooting to the top like a meteor in the early '70s, it seemed as if EJ did his own candle-in-the-wind routine and flickered out.

Another theory: Technology caught up with John, and he did not wear it well. When synthesizers came into fashion, John jumped on board and his piano playing fell by the wayside. I always thought that John's piano work - its heady syncopation, the chunky chords - was the element that gave his music soul. One listen to "Amoreena" from 1971's "Tumbleweed Connection" and it becomes abundantly clear.

The two markedly different sides of Elton John's career are well documented on "To Be Continued . . .," a lushly packaged four-CD compilation. The first two discs are made up of essential stuff. The latter two are not.

The only beef with discs 1 and 2 has to do with the inevitable omissions. "Amoreena" was left out. A sin. In fact, only one song from "Tumbleweed" - in my view, his best album - is included: "Country Comfort."

Neither does the boxed set contain anything from John's scorching live album, "11/17/70," a radio show recorded on that date with a small band.

But most of the essentials are included: "Your Song" (along with a previously unreleased demo), "Pilot," "Levon," "Madman," "Mona Lisas and Mad Hatters," "Bennie and the Jets" (check out the piano), "Harmony," "Rocket Man" and plenty of others.

Some of the post-'75 material bears up a little better nowadays. The ballad "Sorry Seems to be the Hardest Word" is a moving piece of work; "Mama Can't Buy You Love," although a complete cop of the O'Jays, has a certain exuberant kick; "Blue Eyes," with a vocal that calls to mind Elvis Presley, has a nice saloon flavor.

Four new tracks, produced by Don Was, close the set. They range from solid to pedestrian. At least Was features some piano on a couple, although John seems unable to conjure up his previous keyboard magic.

It speaks volumes that John's best latter-era work is 1986's "Live in Australia With the Melbourne Symphony," an album that reprised many of his earlier hits. The concert was recorded shortly before John was scheduled to have thoat surgery. His voice's husky texture, gravelly edge and the use of the lower registers gave the songs new, emotionally charged vitality.