i've played with Opmanger recently and i've found that all around it as a good NMS with a rapid adoption curve due to good built-in vendor/device templates. Business/Network maps with weathermap support it's also a good addition especially when you use xFlow plugin to drill down network congestions. I like ESX support too..simple but effective (if you need deeper/trend/capacity analisys you could use xangati,ecc..) but from infrastructure perspective it's more than enough. Ok now whatmostly preventsmefromadopting it as monitor solution for a couple of my SMB customers is : a) the lack of simple custom monitor (and so template modeling) I mean not SNMP custom monitors but CLI or even WMI monitors since now manual editing DB/XML files is time consuming when you try to model a not included device b) multiple dependency and if possible arbitrary weighed service/monitors (i.e. if01traffic>50% + host2>60% -> group APPX warning alarm) groups where you could add sub-host monitors to built a meta-service/sla group (something like appmanager) c) SNMP trap/Event tranform/mapping (i.e. trap1->trap2 or trap ->host_status_change,event1 to event2 ecc) d) generic script monitor (again..something like appmanager) since sometime you need to be creative =) e) generic WBEM/CIM monitor since HP,IBM,ecc. are using WBEM in their blade infrastructure device and ESXi now will support "only" WBEM to monitor HW health (ok i now that this will go against Opstor since smi-s is CIM/WBEM queryable)
Ah..and a last wish: sub device/host (f.e. interface) objects to business maps!