I transit through FRA fairly frequently. As an SE travelling in J, I realize they do their best to make it simple. My experiences are as follows:

1. FRA is an annoying, dreary, and overcrowded airport - but it generally works OK.
2. The LH lounges are pretty good. Food is better than in many other lounges, and the internet works (though I wish it were free).
3. The AC checkin is out of the way. That being said, I don't recall the signage being a problem (as I said, I generally transit but I often pass by going from a B arrival to a C departure). Maybe there was a systems issue that day?
4. The passport check at the gate is a royal pain, and the staff who do it seem disproportionally unable to deal with any nonstandard cases. By that I mean - if everyone in the line has an EU, US, or Cdn passport, then fine. If there's a bunch of ppl with passports with visas that need checking, or some fine nuance whether they need visas or not, then it becomes a complete shambles for everyone
5. All in all, MUC is clearly better for transferring in Europe than FRA if possible, but give me dependably mildly annoying FRA over chaotic and overcrowded LHR or CDG any time. Though LHR has gotten better.