Background: Other than Tales, I've only played through all of Secret and most of LeChuck's Revenge.
Although there are certainly a few 'throwaway' characters in Tales, I'd say the majority are as memorable as characters in the older games. It's really a matter of taste, I think. Characters that I think are forgettable may hold a special place in someone else's heart.
Not counting returning characters from previous games, my personal favorites so far (in order of appearance) have been Crimpdigit, Trenchfoot, Bugeye, and WP Grindstump.
If I had to pick out characters I cared the least about, I'd have to say Hemlock McGee, McGillicutty, and Tetra. Even these characters that I find less memorable gave good performances. Apparently they can't have been too forgettable or I wouldn't have remembered them at all.