There are many things about 4E that I don't like, but at this point I'm more disappointed in what I see as the wasted potential of 4E than "hating" on it. I see bad math (can't hit the monsters very often so they stick around forever), bad monster design (buckets of hit points, while being insubstantial, regenerating, with an aura that damages and prevents use of healing surges as just one example), and bad encounter design (too much difficult terrain, chokepoints, etc.) as endemic of the system. I think much of this could have been avoided with judicious playtesting, which appears to have not been used sufficiently. It seems that the designers and adventure writers as so concerned with combat not being too "swingy" that they made sure it will last way too long, which creates frustrating, grindy combats that you just want to be over with after beating on a single creature for an hour and it's still up.
Was this from a particular WotC (or 3PP) 4E module?
Or was it something the DM created?