To proclaim extreme pleasure, and/or eventful times normally involving alcohol. It can be used to describe the event, or to share with others the acknowledgement of your positive feelings about a meeting or event.
In question form: 'Did you go for great times last night?'
Exclamation: 'Great times!' - normally followed by clinking glasses together in the traditional 'cheers' motion.
Response to news:
A Guy: 'So did you hook up with xxx last night?'
Laid Guy: 'Yup'
A Guy: 'Great times'