I fly IB fairly often, and find them pretty much the same as any other airline, in the sense that the experience will range from sublime to abysmal, depending on cabin class, crew, aircraft type, day or night flight, their mood, my mood, companion, etc. The best IB of the day will run rings around the worst LA/AA/BA/etc., and viceversa, of course.

I would not choose IB, but would not avoid them at all cost either, except for FFP issues.

[Three days ago I flew EZE-MAD with IB: great plane (340-600), great crew, decent food/drinks, cheerful atmosphere, everything right,... until two babies started to cry in unison and in crescendo; from then on several passengers lost their cool, the FAs reverted to dragons, the food/drinks got harder to get, even the movie broke down, for pete's sake, and a fine flight turned into a 12 hour nightmare]