In theory, EFI is supposed to have a shell available, which could make diagnosing low-level problems easier. This is of course assuming that the manufacturers can be arsed to include it alongside their 'point and click guis'.
In almost every case, you'll be able to install your own EFI modules, including a shell -- I haven't seen an implementation yet where you couldn't. It's amazing how much flexibility you have with compliant EFI implementations.