The problems I see with economics as a discipline are threefold (and bear in mind I'm no expert, so take this with a grain of salt):

First, it seems to have at its core the idea that humans are rational creatures who optimize their choices when it comes to money, and thus will behave in predictable ways. In contrast, there's ample evidence that people are irrational in many situations. It's a very shaky foundation.

Second, it's trying to explain a chaotic system. The number of variables and their interactions are so complicated as to be nearly impossible to model, especially when no-one understands the nature of the variables or their interactions in detail.

Third, the sum of the first two problems is that you end up with a discipline where opposing models can have equal theoretical merit, and can be argued for equally convincingly. That makes it interesting and frustrating at the same time, and the overall impression is that neither side really understands things as well as they claim to.