Keep in mind that reports in Operations Manager are based on sample collections which are then rolled-up into averages. For example, the Operations Manager server daily history for LUN latency is an average over every 15 minutes. Monthly history is an average that covers every 8 hours. So you're looking at numbers which may include spikes that throw-off the average. You'd be better off using Performance Advisor to view your historical LUN latency as it does not roll-up counters into averages. It shows each counter it collects, usualy on 1 minute intervals. Then you can define thresholds and alarms to notify you when latency exceeds a certain value.
So, to answer your question about how to interpret them. As you probably know, latency is a measure of how long it takes the object (LUN, volume, aggregate, or disk) to respond to a I/O request. There is always some amount of mechanical latency on a physical disk drive, but latency can also caused by other factors. The generally accepted industry-standard for disk latency is 20 ms or less, but it truly depends on the application and its requirements. Some applications are more or less tolerant of disk latency.
For performance monitoring, I would focus on the LUNs that make-up your ESX datastore. There are canned views in Performance Advisor that show latency for LUNs. If the LUN latency is greater than 15 or 20 ms for an extended period of time, I would suggest you start working your way down from the logical objects to the physical. From the LUN, I would next look at the volume the LUNs are in. If its latenct is high as well, I would then look at the aggregate the volume is in. Perhaps the aggregate doesn't have enough disks to meet the I/O requests. Perhaps there are other volumes in the same aggregate that are so busy, they're impacting the performance of your ESX LUNs. If the aggregate has enough disks so that it should be performing well, the controller's CPU could be at its limit.
This is a very broad topic. Let me know what other questions you have and we will go from there.