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First off, I think the poster is extremely appealing - the colors and composition are great. The only things that immediately grab my attention as minor negatives are:
1) The strength of the shadows from the light cups seems to beg for a little shading on the top left. That big branch (and presumably tree) in the foreground would be casting a bit of a shadow on the traffic light, and a bit of shadow would also help to pop the bright green of the leaf from the similarly-toned yellow behind it.
2) The compositing on the recycle logo is throwing me off a bit - everything has such consistent shading and implied depth that the recycle logo feels extra flat by comparison. I think I'd try adding a tiny bit of spherize-curvature to the logo and then adjust the transparency effects to allow more of the texture of the light bulb to be visible so that it felt like part of the background rather than a limbo element sandwiched in an impossible space.
That said, it's very appealing and these are nitpickity.
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I'd hesitate to try blending the Recycle logo (or even the text) with the traffic light. Agreed, it would appear more "real" but I think it would lose a lot of its punch and clarity.