I do know that the old cameras only had a shallow width of picture - these show a hell of a lot more of the houses opposite but the old ones were only 2mp and one was 3 or 4.
That would make a significant difference. If you've gone to a wider field of view then the resolution would need to be much higher to give the same picture detail as before.
For example going from a 6mm (narrower) to 2.8mm (wider) would require between 2.5 to 3 times the resolution to give the same detail. A 4mm to 2.8mm requires about double the resolution. There are a lot of other factors such as lens quality, sensor size but this field of view change means 4mp won't be showing more and probably less detail than your older cameras. As mentioned before I cannot comment on how the NVR or its settings, zoom method could further impact the output picture as I gave up on NVRs some time ago.
One other comment is regarding your two ColorVu cameras in case you notice it. These won't have sharp focus as close to the camera as cameras that use IR at night due to the aperture of the lens. A standard camera is sharp from very close up (1m or less) but the ColorVu are only in focus from between about 2m and 7m depending on the lens (wider angle being better than narrow in this case).