Residence Inn San Diego Sorrento Mesa-Sorrento Valley

I had stopped for a stay in San Diego at the Marriott Category 4 Residence Inn San Diego Sorrento Mesa Sorrento Valley. While this was a decent hotel to stay at, I am often left puzzled at how Marriott determines their categories as I felt this was a huge difference from the splendid experience I had at the Courtyard Seoul Times Square, now a hotel in the same category as this one.