I think the biggest thing you’re missing is the actual aluminum texture of the can. The renders look great, but cans shouldn’t be that glossy. Your best bet would be to find some aluminum objects and use them as references for texturing.
If you look at these images:
I found these at http://images.google.com. You can find more examples there. Anyway, if you look closely, there’s a brushed/scraped look to the aluminum. Now, when you move down to the labeling, most the labeling can usually hide the scraped look from far away. but it will still be minimally visible when you look at a can close-up. So, the parts that haven’t been painted should not be as shiny as the part of the can that’s labeled.
As for the label itself, you might want to take it and make it into a hi-res image, then run it through a Photoshop filter like Color Halftone, and then size it down. It’s basically the same method the companies use for making their can’s labels, as less tones make for cheaper printing costs. Or something like that. Anyway, if you look close at most pop can labels, you can see how speckled it is.
And for reflections, I’d recommend having the reflections blurred/streaked in a manner similar to how aluminum reflects. The reflections can be a lot more clear on the label part, especially with the way companies seem to make the labels a lot shinier on cans these days. But for stuff like the top and the bottom, I’d definitely soften the reflections a lot.
The best way to do this–I did this myself before I replied to the thread–would be to just find a can, and take it somewhere with some light, and hold it up and watch how the various parts of it reflect the surrounding environment, including orientation.
That’s about the best advice an amateur like myself can give. Hope some of it helps.