Monetary union without a fiscal union. It is a slightly odd position, but most countries aren't ready for the sovereignty transfer implied by centralising fiscal policy. The politics of paying for Greek pensions just doesn't work.
The idea of the euro is convenient, but since the crisis of 2007-2009 + various (Greek) scares, it's devolved into a "cake and eat it" situation.
A country cannot devaluate its currency (Sweden still has this freedom if it so wanted).
I'm not sure what the solution is, but to start, I would homogenize corporate tax rates, and discourage tax-shopping inside the EU.