Most of the time, the queries that are suffering because of the new cardinality estimator have other issues that can be addressed (or the architecture is off). Frequently the best fix is to identify what's wrong around the query and address that. In rare cases the issue is that the old estimation resulted in better plans and better performance, but that's rare.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning