They're great for your knees, back, and butt. The hill issue can be solved with patience and good gearing, and you make it up on the downhill (much more aerodynamic).
Recumbent advocates like to point out that they're banned from the Tour de France because on average they are faster and more efficient.
I've not ridden one much, but a lot of people around here are dedicated converts. I can't speak to the commuting/visibility issue, except to note that it's not as though you're super visible on a normal bike.
Personally, I like to ride cheaper beater bikes, and do stupider things; at the same time, I'm young enough that my knees, back, and butt can take it.