Maybe it's because you're shooting with a Nikon? Hahah, just kidding.
But I've noticed with Nikons that if you don't use a Nikor lens, it just doesn't look right. Was this lens a Nikor?
And instead of sacrificing your depth of field because of low light, try bumping up your ISO instead of your aperture. Nikon is famous for quality at really high ISOs, and it's not like you're putting any of your pictures on billboards, so you don't need a really high quality image, just one that'll look good at screen resolution. This way you can shoot at f/8 @ 1/125th with 1600 ISO maybe instead of f/1.8 @ 1/60th with 100 ISO? (Just guessing at what those numbers are XD)