General:
* General
* Comprehensive
* Total
* Global
* In general
* On the whole
* In summary
* In conclusion
* In all
* By and large
Specific:
* Aggregate (for numbers or data)
* Collective (for groups or things)
* Total (for amounts)
* Comprehensive (for scope or coverage)
Informal:
* All in all
* To sum up
* Bottom line
The best synonym for "overall" will depend on the specific context of your sentence. Consider what nuance you want to convey and choose the synonym that best fits your meaning.