Here are some additional thoughts for you:
The Assassin and the Necromancer both have diverse sets of skills that help to make underpowered characters work. Consider the Necro's curses as a base capability - decrepify, amp damage, dim vision, confuse, attract, etc. Those one point wonders represent a lot of capability that can save an otherwise underpowered build so if there are other Necro skills that appeal to you, you might be able to construct a viable build.
Same with Assassin; 1 point in Mind Blast and Cloak of Shadows can create a lot of crowd control and 4-5 points in BOS or Fade increases survivability against melee/physical and elemental attackers. So you can create a fun-to-play assassin with those as a base - just think about which attacks you want.
The Barb is always underpowered, it seems, and needs to be tightly constructed around a master plan for skill points and equipment. The singing Barb isn't as much as fun as the Assassin to play. Ditto for the Amazon, she's always underpowered (with the notable exception of the overpowered LF Amazon) and every decision on skill points, mercs and equipment is critical for success. A Tankazon wearing leather-only armor with a 2-H staff as a weapon has always sounded attractive to me. Or (my own idea) a Barb who must wear a different Set of equipment (Sigon's, Milabrega's, Tal Rasha's, etc.) for each of the 15 Acts and 3 Cow Farms that he plays.
The Sorceress is fun to play but is Synergy City. Choose a main Sorc skill and its synergies, budget your remaining skill points for a backup attack and/or defense skills and go play. I'm playing a Charged Boltress now according to the guide and its fun.
I hope this helps stimulate you. Let us know what you decide!