Nothing is special about the Pits; it's just one of the more popular lvl 85 areas (actually, "popular" is an understatement. "Severly overhyped" describes it better).
The pit combines a few useful things, especially for characters that can't handle River of Flame/Chaos Sanctuary or the Worldstone Keep:
- it's area level 85; the highest (relevant) level
- therefore monsters there can drop all sets, uniques, runes and base items
- The Pit is reasonably large, with multiple boss packs
- The Pit Level 2 has multiple bosspacks crammed into a small area
- The Pit is only populated with Act 1 monsters
The first 3 aren't unique to the Pit, but the last two pretty much are.
I actually prefer RoF/CS/WSK (lvl 85 as well) over the Pits, because of the act bosses at the end. Also, Durance/Mephisto is pretty good; Bremt Sparkfist and the other council guys in Durance-4 are pretty much like the "multiple bosspacks crammed into a small area" situation, "but" Durance is "only" lvl 83. But again, act boss at the end is always a plus.
Pit Level 2 has a sparkling chest, but these tend to drop rubbish all the time. Doesn't compare to act bosses, IMHO.