I can very much see your point of view. I guess you don't play it with multiple friends and never tried a harder difficulty? Personally I would find playing this on my own pretty boring as well and see DIII as one of the prime examples of a game type that should always be enjoyed coop, with the rare solo farm in-between.
I'm currently progressing with two [HC]characters through Nightmare, not particularly in a rush, nor having a preference for one character. One is a Demon Hunter with a focus on survivability/damage and the other a Witch Doctor with a focus on survivability/support. I've not set foot in Hell on any character just yet, something a lot of people probably find strange, but I'm enjoying my game play, slowly, and enjoying fighting with constant threat of death.
It's quite fun when you progress and find yourself no longer fearing A1 t/m 2 and suddenly almost getting nuked in A3. The increase in difficulty is quite apparent, especially to characters that simply can't die, because that would be like, fatal.
So far Blizzard has exceeded my expectations. They made it hard, but not too hard. I'm quite sure Inferno is not too hard, it simply requires adapting. Albeit those damage "spikes" might obviously affect anyone. That said, it will be a month or more before we even consider entering Inferno. Strangely, I'm hoping that it won't get nerfed, but only fixed if Blizzard finds those spikes to be undesired.