I've run 4 solos (Sorcerer, Wizard Slayer, Fighter/Mage, Fighter/Thief) and 6 parties. I tend to flip between two savegames (right now, between a Totemic Druid and a game with a Cleric/Ranger as my main character.) I find there more than enough variation. If you're still having problems with fun for party games, have you ever tried it on Insane difficulty, with various mods (Tactics, Improved Battles, yada yada yada)? Adds a whole new dimension. Eventually you'll be able to solo through them, but they're lots of fun with parties. Also, try mods like Kelsey, Chloe and Solaufein, or even GBlucher's alternate NPCs, to try out different classes. A good site to check out for some fun party ideas is
All Classes at PlanetBaldursGate. They have an example of a fun, themed party for each character class. Check it out.