I'd add a bassline and maybe another percussive instrument... hi hats, congas... something to drive the beat. But I'd definitely put a bassline on a slow groover like this. It will add to the drama.
And think about layering those strings. Maybe add another type of string patch or layer it with another intrument capable of playing long sustaining notes. But I think the string patch needs some help.
A thicker drum kit might also be in order. With sparse tracks such as this, it's not a bad idea to have each element be heavier. Try layering the kick & snare to get something with more weight.
I'd also add some contrast for a chorus... maybe vary the groove a bit, and go to a new chord or 2.
Lastly, I'd sprinkle a little candy on it. A slow groove like that is begging for some atmospheric effects creeping in every few bars or so.
Lyrics on top of that, and you have a pretty full track, unless this is going to be an instrumental. If it is going to be an instrumental piece, I think it needs to develop more. Take a listen to some DJ Shadow to see how he might develop a slow groove like this.
You have a nice foundation to build on.
The Groove baby, the groove...