I've been using Logos 4 for a while, and I have some suggestions.
1) If I look up a word in BDAG and rollover the verses that are listed it will give me the verse in my default Bible. If I set my default Bible to ESV it is sometimes hard to figure out which English word corresponds to the Greek word I am reading about (often there are synonyms in the sentence), but if I set my default version to NA27 it takes me longer to get a sense of what the verse says. I tried to set my default version to an interlinear but it never gives me both the Greek and the English. What I would really like is the ability to give a default and a SECONDARY and have it show one above the other - so the entire verse would be given in Greek in the popup and then in English below and I could look at whichever I want to see. This would help me tremendously.
2) I have been highly disappointed with the lack of textual apparatus in the NA27. I understand that I could purchase the Stuttgart Electronic Study Bible, but shouldn't this really be a part of NA27? It's not really NA27 if you don't give us the apparatus from the book. I also wonder (even if I purchased the SESB) if it would be possible for me when I rollover a verse reference to see not only the verse but also the critical apparatus. This is especially important when I'm looking at an entry in BDAG and it says that a word occurs in a variant reading of a particular verse. Right now if I roll over it will show me the verse without the word I'm looking for. I'd like to see what variant reading has it and where in the sentence it occurs.
Otherwise Logos 4 works great. I look forward to seeing how it develops in the future!