Quality of a landing page?

What exactly are you trying to figure out? How well a landing page is actually performing, or how relevant Google determines it to be for a particular keyword? A low quality score (in adwords) could be the result of several things, poor keyword selection or matching type.

I think looking at the landing pages conversion rate at the keyword level will best estimate the "quality" of a landing page. Compare it with other sources of traffic (organic, direct, etc) in terms of conversion rates and cost per conversion.

If you just want to see the AdWords Quality Score, you can view each quality score by going into your ad group, looking at the keyword list, selecting "Show Quality Score" from the Show/Hide list.