Well done you have (hopefully) finished the project, within the agreed constraints of time, cost and quality. The benefits are just a step away. The end of the project provides an opportunity to formally review how things went, what would work well again and what you would do differently next time.
Compare the final cost, timescale, scope and expected benefits with those outlined in the original Project Proposal. Consider the impact of approved changes.
Finally time for that glass of Champagne, or nice cup of tea, whatever is your bag.