I'd say you're well on your way! Next step is to reduce some of the colors you have going on. Samurai jack used a very heavy masking-based lineless art style, meaning things were typically layered heavily and didn't have any outlines to them.
You can see this in all shots of the show, like here:
Note how the only times lines happen are when they need to put in a detail, like jack's face wrinkles or folds in his Kimono.
When you're emulating this art style, try to think in terms of blocks of flat colors rather than in terms of linework! Try to reduce his outfit to two colors, a light grey and a middle grey.
I'd reccomend redrawing that entirely too, samurai jack really rides on its flowy and heavily-geometric art style and you really need to draw from that from core to base.
Finally, I actually think the original expression was better! Jack tends more towards stern glares and your original expression gave him more of a wary look.
More in terms of general advice, you may benefit pretty well from some gesture drawings! quickposes.com is my website of choice, but the technique is excellent for loosening up your poses.
