(I typed this up before the replies, so none of this takes the new information into account.)
Whether it's game-ready depends on the look of the game xP That's a meaningless question without context.
I think you did a great job on the outline. It looks like an actual couch and not just some simplified, abstract idea of one. However, I feel the colours and shading fall short.
The greens are very dull because all of them have the exact same hue and nearly the same saturation. Varying up the hue (and to a lesser degree, saturation) helps give the colours more life. Hue-shifting the shadows and highlights on all the objects in a scene towards the same colours can also make the scene feel more unified, as it gives the impression of the objects being lit by the same light sources. If you just keep everything its own hue, all the objects will feel disjointed, like they don't belong together.
The shadows are "pillow shading" - you're placing dark pixels around the edges of shapes, rather than choosing a light source and shading according to that. This also plays into objects looking disjointed, and it also makes them look very flat, as shadows are important in creating a sense of volume.
The dithering along the bottom cuts straightly off into the lightest colour, which looks strange. Dithering mainly does one thing: it creates transitional "colours" when using an extra colour isn't something you can or want to do. Using it on its own rather than as a transition just creates meaningless texture.
Here's an edit that shifts the shadows towards red. I chose red because couches are usually found in interiors, which often have many warm-coloured objects and therefore a warm ambient light. Hue-shifting towards blue or purple would've been fine too.
It's a minor change, but it makes it look more interesting.
In this edit, I redid the shadows to follow a light source that is above the couch.
I got rid of some of your lineart where it was just adding too much detail, namely at the top of the seat, and the little Xs, which I understood as those dents where the fabric is fixed in place, creating a segmented surface on the back of the couch. I created the look of those segments with shadows instead.
Since the light is coming from above, I removed the shadows from the top edge. However, you might notice there are still some darker pixels there - that's anti-aliasing so that the outline doesn't look quite as harsh against the light green.
You might also notice I didn't use any dithering. I didn't feel there was a need for it, since there are plenty of colours, and couches tend to have a relatively smooth surface, whereas dithering creates a rough look.