I have a GTL. I'm coming off 4 K12LTs ('00, '02, '05, '06) and an R12RT ('09). Unfortunately, most of my riding is daily commuting in heavy urban/suburban traffic.
I often said the LT was an ideal commuter -- lots of storage space (briefcase, files, raingear, suitcoat, et., etc.), great weather protection and lots of nice to have features (heated gear, radio, etc.)
The GTL is different than the LT, but every bit as good as the LT in this application, with better handling due to both the Duolever and the 100 lb. weight loss.
Downsides: The trunk is not quite as large. There is a small amount of heat on the left shin above 90F. Wind protection at 70 mph is about 95% of the LT's. Not as much room under the skin for add-ons (fuse boxes, etc.). The lack of a wired audio option (Bluetooth only, and I'm not convinced the intercom will be better, as it's not clear to me yet that it is VOX actuated (as opposed to requiring a button push every time you want to talk) -- I haven't received my BMW Bluetooth units yet, so can't comment).
Upsides: Handling -- I've never ridden a bike this size with such confidence-inspiring handling -- the LT can certainly dance well, but the K16 takes it to a new level. Power -- the LT's great weakness IMO, was the lack of low-end grunt, even after the '05 revision -- that is not an issue with the GTL; there's so much torque that you forget to downshift. Electronics integration -- a bit of a learning curve, but quickly adapted to. Large, removable saddlebags; easier-to-remove topcase. Virtually nothing given up to the LT -- central locking, lighted topcase (now with struts to hold up the lid), good passenger accommodations.
The GTL is, to me, 1/2 way between the LT and and RT, with a lovely engine smoothness and excellent handling -- hard to ask for more.