The biggest issue I see with it is that when trying to do trade deals or any deal with the likes of Australia, USA, China, India, etc. you need all the 28 nations to agree on what is put forward, which either takes time or doesn't happen at all, where if it's just 1 nation discussing with 1 nation agreement is far easier.
Also, the Italy situation doesn't sit comfortably, although I understand why the EU have made their stance, but should they really interfering in how they set their budget. In theory, and appreciate we aren't in the same boat as Italy, but if Labour got in and decided to borrow heavily to get the public sector in a nice position, the EU could prevent it happening.