I think badmouthing the developer who came before you is not good. But, a long succession of good developers, can jointly produce a codebase which is awful. Part of this is simply the fact that it has changed hands many times. Part of it is decisions made that the developers were not able to control. There are many other possible reasons. But, although most developers are trying to do a good job, and I think it is bad form to badmouth the developer before you, it is often quite simply the case that a large and old codebase is, in fact, truly awful.