You’ve got a really nice start here. The modeling looks really good, and the textures are mapped very nicely.
Which renderer are you using? It’s kinda hard to tell.
Just at first glance, it looks like there isn’t any ambient occlusion going on, or very little. It that that in itself would help a lot. If you’re using Cycles, you might want to try turning down the energy of your fill lamps down, or scaling them down in size. If you’re not using Cycles, I would highly recommend that you switch. If you have questions on how to setup materials in Cycles, it just so happens that Jonathan Williamson posted a new tutorial on that subject this morning. blendercookie.com
While I think the knife is pretty cool. I can’t recall seeing a knife with that particular shape. I think you could add some realism just by providing shapes that people are used to seeing in real life. That btw is one of the basic tenants of usability in design.
Like Kramon said, the lime looks very flat. You really should have some reflections going on, not to mention a normal map of some description. I would probably do the same to the window frame, the counter top, the walls, and the knife handle. I found this nice picture:
You might also consider adding a cutting board or something.
Like I said though, great start! Sorry about all of the nitpicking, but you did invite us to go ahead