For the last few years I have been playing in a exploration sandbox campaign comprised of a D-team and It has been my favorite so far (20 point buy full BAB classes only, slow advancement). Our players consist of:
Fighter(Lorewarden) - focusing on tripping with whips (could trip nearly anything large or smaller)
Fighter - focusing on disarming (damn skeletons are more deadly if you disarm them)
Fighter - focusing on archery.
Cavalier - halfling riding on an elephant.
Ranger - mounted, our primary damage dealer.
Using strong tactics, teamwork and making heavy use of attacks of opportunity (everyone but the archer eventually had combat reflexes) we actually tore through more enemies than we thought we would be able to handle. The DM certainly challenged us, often using large amounts of enemies (primarily orcs and undead) over a few more powerful enemies.
The campaign had a reasonable role-play aspect and involved heavily on the town we were helping develop with the downtime rules, which eventually expanded into the kingdom building rules.
While healing was a problem, due to teamwork we tended not to take too much damage and we got by with a conservative amount of magical healing. Magical items were not commonplace and we got by on what we found.
I have not been in any other game that the players have worked so well together or had nearly as much fun.