Been on her 8 or so times. Definitely showing her age. Don't be at all surprised if the TV in your room doesn't work (had that problem on the last trip) or problems with the shower (door, drain, etc.). As mentioned, the pool-side screen has been covered since lasy year (with no plans to fix) but hasn't actually worked correctly for at least 3-4 years (pixels out and blocks of "differnt" colors where they had previously tried to fix areas). If you look around, you will find rust, bad carpets, etc but nothing bad eneough to make it not worth the trip.
The BIGGEST variable on Liberty is the staff. Liberty is a "trainer" ship for the bigger (Quantum/Oasis class) ships. My experience (and knowledge based on talking with many of the staff) is that you will see more "brand-new" staff on this ship (or class of ship) than just about any other. They do a staff rotation something like every 60 or 90 days. New staff start off in the Windjammer (so they can work on their speaking/interaction skills), then go to either room-service or side restaurants. As such, you can have great service in the Windjammer one week and it be terrible the next (since the trained staff have rolled to another area of the ship and been replaced by newbies). You would think that they would rotate folks gradually (i.e., a few each week) but that is not the case since they rotate in large blocks (i.e., 1/3 - 1/2 of the Windjammer wait-staff all at once). Becasue of this, don't be at all surprised to hear someone say "wow, service sucked" and then someone else say "what? I was on the week before and It was fantastic. You must be too picky".