There are no trick recipes you can use to spit out the competence of a database. There are more metrics that can be employed to aid you ascertain if one environs of the database is playing well or not. I'd start with Statspack (Oracle 8i and 9i) or ADDM (Oracle 10g). You can get descriptions on more assorted characteristics of the database performance. For instance, you can observe if advancing your buffer cache will aid database performance.
But no subject what you perform to the database, no of it makes any divergence if your end users are not receiving the recital they expect. In the end, the only accurate way to evaluate database competence is to chat to your end users. Are they cheerful with the database performance? If not, which characteristics of the request for paid job are playing weakly in their opinion? I can draft scripts all day long which give me a number and make a determination on that number on how well the database is performing. But if the end users are not cheerful, my number and its smashing purpose perform not intend anything.