Until 1974, the Electric Light Orchestra had managed only modest hits with 'Showdown' and a cover of Chuck Berry's 'Roll Over Beethoven.' If those songs only pushed the door open slightly, the transitional 'Eldorado' would kick it wide open.

The project was, for all intents and purposes, a concept album, both lyrically and musically. Jeff Lynne and company make full use of the studio as instrument and put together a warm and inviting album that, 40 years on, stands as a bold indicator of future successes -- even as it shows how far Lynne still had to go.

That starts, of course, with Lynne's passion for all things Beatles. With 'Eldorado,' he wears that influence on his sleeve. As the slightly ominous 'Eldorado Overture' kicks in, the listener knows this is not just a rock band with strings, but rather an honest-to-goodness rock and roll orchestra at play. The overture gives way to what is arguably Lynne's finest composition, 'Can't Get It Out of My Head' -- though it remains such a blatant Beatles rip off that it might makehave Noel Gallagher blush.

Lynne, however, not only pulls it off, but in the process creates a masterpiece. The result is quite possibly the best Beatles-drenched song this side of 'Cheese And Onions.'

A whirlwind of strings then cascade into a loud wall of guitars, as 'Boy Blue' picks up the pace a bit. It's basically a three-chord rocker based on a simple riff, but as played by an orchestra. From there, Lynne continues developing trademarks he would rely on through the years, even as he makes some youthful mistakes. 'Laredo Tornado,' for instance, begins with a George Harrison-like guitar line, unfolding into a soulful little number. The appearance of a clavinet, however, sticks out. Lynne was not a funky soul and it sounds out of place. Aside from that minor squabble, this is a powerful track that uses the dynamics of the orchestra to full effect.

'Poor Boy' suffers a similar fate. With a slight Roy Orbison vibe to it, the use of the acoustic guitar as driving force would become a Lynne staple over the years -- in particular on their work together in the Traveling Wilburys. Lynne is still getting the hang of balancing strings, horns and choral vocals, however, and things get a bit cluttered.

Watch to ELO Perform 'Poor Boy'

'Mister Kingdom' returns to Lynne's now-familiar Beatle-isms, copping a melody that's awfully similar to 'Across The Universe.' Still, it works perfectly here. In fact, 'Mister Kingdom' may be as good a representation of the ELO sound as one could find. 'Nobody's Child' has a slow bluesy drag to it that sets itself off from the rest of the album nicely. It struggles not to sound like Elton John covering the Bee Gees, and mostly succeeds.

Meanwhile, 'Illusions In G Minor' finds Lynne taking the basic Berry-style groove and layering it with ELO's decade-defining sound, never losing the rock and roll core thanks to a killer guitar break. In constrast with 'Poor Boy,' Lynne achieves a delicate balance between soaring symphonics and straight-ahead rock, constructing a deep-cut highlight.

The title song and its adjoining finale finish things up on yet another Beatles-esque note, albeit slightly less obviously this time. His mid-paced ballad wraps up the concept, both in words and music, followed by a closing section brings together themes heard throughout.

It seemed, finally, that things were coming together for ELO. Powered by a Top 10 showing for 'Can't Get It Out of My Head,' the No. 16 hit 'Eldorado' would go gold -- then the Electric Light Orchestra's best-ever showing in the U.S.