As a frequent visitor to Central over the years I haven't seen any real improvements to signs and visitor information. In comparison to major rail stations visited overseas ( recently Zurich, Rome, St Pancreas, etc, etc) where signs are clearly visible and easily understood. I always think about overseas visitors trying to negotiate Central when I am at Central. Try the Airport -> Northern line connection when English may not be ( and even if it is) your first language. Needless to say anything about the general state of the trains once your eventually reach one.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.