The Foundation sees this as a contradiction to the EU’s own interoperability goals. Although XLSX is standardized as OOXML according to ISO/IEC 29500, Microsoft’s implementations often deviate from the specifications. Furthermore, features often change undocumented, which complicates compatibility with open-source software such as LibreOffice.
I think it’s perfectly well suited to spreadsheet. It’s more-or-less perfect for tabular human-readable data. If you want to embed fancy things like OLE objecta and ActiveX controls and helpful animated characters then you may well be better served with another format.