Cool
It's not a wierd slow riff ! :P It's more like an 8-bar, 3 chord progression. 2 bars for the first two chords and on the 3rd chord played, it is held out for 4 bars.
also, having a slower tempo commonly found without drums and there being an acoustic sounding rhythm with an electric/electricacoustic sounding lead over the top matching the chord changes.
It's not wierd at all... but it is quite beautiful with absolutely no added effects at all.
great job, melody is cracking.