There’s a constant temptation to categorize music into appropriate genres, because of course that’s supposed to instantly tell you what to expect. One of my personal favorites is guy-with-acoustic-guitar, an unofficial genre with significant breadth and prominence, which promises tranquility and comfort akin to summer Sundays.

Two new releases fit under this acoustic genre, but of course they are two different and distinct creatures. Jack Johnson’s third LP, “In Between Dreams,” is an ode to simplicity and buoyant, campfire-friendly romanticism. It’s exactly the kind of music that a surfer living in Hawaii would make — you can practically hear the tradewinds and the lapping waves. “Dreams” is another typical Johnson production, which means it’s both very good and sorely monotonous. But no one ever said he was supposed to be arty.

On the other hand, singer-songwriter M. Ward’s “Transistor Radio” is a somber folk album and much more multifaceted. Playing the kind of music that would be heard from someone’s porch in South Carolina, Ward takes himself more seriously than Johnson. (He dedicates the album to “the last of the remaining independent radio stations.”) There’s a thematic artistic weariness expressed incredibly well by Ward, though “Transistor” lacks total cohesiveness and lacks the perfection of its predecessor, 2001’s masterful “Transfiguration of Vincent.”

You can say lots of things about Jack Johnson, but you can’t say he’s inconsistent. Drawing from reggae and bluesy influences, the album abounds with Johnson’s characteristically melodic, catchy and upbeat tunes. They all burst with optimism (“Rain all day and I don’t mind”), and carry a carefree swing that only a cynic or a snob could resist.

On the perfectly enjoyable opener “Better Together,” Johnson smoothly sings in his simultaneously rhythmic and melodious style over a bouncy acoustic guitar. Another highlight is “Belle,” on which he sings in Spanish and French over a bossa nova guitar riff. In contrast, “Sitting Waiting, Wishing,” the first single off of “Dreams,” is disappointing. The surprisingly whiny track has an intolerably droning chorus: “Must I always be waiting, waiting on you?/ Must I always be playing, playing your fool?”

Johnson adds to the guy-and-his-guitar formula by throwing in a little percussion and piano, which enhances the ultra-chill ambiance appeal. A case in point is “Breakdown,” which originally appeared on Handsome Boy Modeling School’s “White People” as a drum machine-powered gem. Here it’s quieted down here to just a soft ukulele and drums, which sounds wonderfully organic (you can hear Johnson knocking the beat on his uke), albeit less powerful.

The best on “Dreams” doesn’t vary much from the worst on “Dreams,” but no one is really expecting Johnson to diverge much from his wildly successful feel-good formula. As frustrating as monotony on an album may be, his song-writing is too catchy to accuse the album of mediocrity. “Dreams” has much stronger tunes than 2003’s forgettable “On and On,” but lags behind Johnson’s lovely debut, 2001’s “Brushfire Fairytales.”

On a similar acoustic scale, California-born, Oregon-based M. Ward’s music has a wistful, quietly reflective feel. On the excellent “Transistor Radio,” his fourth album, Ward consoles alienation with a sober optimism (at least compared to Johnson’s). He screams sincerity — or rather, in his gravelly singsong voice, he softly croons it.

“You Still Believe in Me,” the album’s opener, sets a rich tone. The song, which layers wonderfully developed acoustic guitars into a dynamic crescendo, is a purely instrumental cover of the Beach Boys classic. Like the rest of the album, which is chock full of instrumentals, what could easily be boring is instead luminous and exciting.

Ward excels in championing a classically antique, even timeless sound with doo-wop harmonies, bluegrass roots, slide guitar and grainy production. “Paul’s Song,” with its soulful steely-guitar, is a reminder of country music integrity in pre-corporate Nashville. On “Fuel For Fire,” Ward waxes poetic with admirable emotional depth. The unabashed loner ballad bestrides teary slumber with a radiant consolidation. The only song on the album that has more sheer pathos is the closer, “Well-Tempered Clavier,” a solo acoustic rendition (except for a quietly singing background synthesizer) of Bach’s masterpiece.

“One Life Away,” is a hazy, lo-fi tune (or, more accurately, it has a purposefully old-school radio quality) that features My Morning Jacket’s Jim James, whose falsetto is almost angelic under Ward’s. The song has the earnest folkiness of a Hank Williams song, like many of the best acoustic songs on “Transistor” do. Yet, if the album is intended to be a salute to childhood memories of utopian radio, it lacks continuity and the compositions are subtly disorganized; right after “Life” is the relatively weak “Sweethearts on Parade,” a discordant, noisy ode to ’60s psychedelia.

Perhaps it’s because of Ward’s wariness of mainstream pop, but “Transistor” does not have the memorable hooks or the melodic engagement of the impeccable “Transfiguration.” Nevertheless, the album has a wealth of thought, emotion and intelligence. While “Radio” needs repeated listens to fully appreciate, the dulcet catchiness of Johnson’s “Dreams” makes it instantly accessible. The latter singer-songwriter might be easier to like, but M. Ward possesses genuine depth that is infinitely worth exploring.