If you actually mean the D300, well that's in a totlaly different class. Much better build quality (magnesium vs. plastic/aluminum), far more features, etc. And a much higher price tag to match. However I assume you meant the entry level Nikon D3000 ? This is much more comparable to the Olympus E-450. Although the Nikon still has a superior autofocus system, larger viewfinder (even if it's among the smallest of any Nikon dSLR), and better low light performance. Nikon also has a much broader selection of lenses though not all are fully functional on the D3000.In its favor the E-450 does have Live View (eg. the option to compose your shots via the LCD, with some limitations). This is not something I would recommend using normally, but it can be rather useful feature when shooting from a tripod. Nikon has also equipped many of their new dSLRs with this feature, but not the D3000.