If by chance anyone is interested, I have "studied" the development of reggae sound pretty explicitly (i.e. rather than just casual observation), so I can offer a few examples to start hearing what reggae was in its earliest years.

The following track is mostly the rhythmic groove known as "rocksteady" (which was still in effect in 1968), however it is overlaid with some elements —most notably the organ part — that foreshadow "reggay." The original instrumental groove was created in early 1968 and produced by Clancy Eccles.

"C.N. Express"

The next track was produced at Studio One with their session band, Sound Dimension. The guitar sound was new, using a delay pedal to give the "double" sound. There are still elements of rocksteady, but occasional syncopations and business in the drums depart from the norm of rocksteady.

"Nanny Goat"

This track produced with Harry J's group, in a way, combines the new elements of the preceding, namely the heavy "bubble" played on the organ, and the regular double-hits of the guitar.

"No More Heartache"

This later Clancy Eccles track moves the development forward with a drum rhythm that is a complete departure from rocksteady. While the preceding examples could all be called reggae, this track and ones like it marked the real turn into new stylistic territory.

"Don't Brag Don't Boast"

There's lots more variety, and all that is just in one year, 1968. The reggae grooves continue to develop in the hands of a half-dozen studio bands, and they will get more different before they get more similar to the groove known to international/non-Jamaican audiences.

Early reggae rhythms were energetic and/or intense, not languid. However, as mentioned earlier, live bands (especially outside Jamaica) that would be inspired by the cultural movement exemplified by later Bob Marley, have tended to adopt a sparser, perhaps more simplistic and softer groove. Such groups are essentially anachronistic, since after Marley's death in 1981 most of the Jamaican music scene shifted to gritty dancehall music, which in the beginning (in terms of rhythm) was first largely a throwback to rocksteady and thereafter developed into completely new rhythms. Few latter day live bands seem to master (or bother with?) earlier/other forms of reggae rhythm, but one that has done a great job with this is the California-based group The Aggrolites. Here they show their mastery of a 1969/70 era groove:

"Mr. Misery"

I included that last example, though I could have chosen hundreds of other examples of period music played by Jamaicans, to illustrate that non-Jamaicans can get on fine mastering the Jamaican rhythms -- that it's all about putting all the parts together. Reggae is not some plain off-beat guitar thing! Nor is much of it droopy, stoned-out music for people about to fall asleep and off their stool.