Incredible is an adjective. Some synonyms are amazing, spontaneous, great, good, fantastic, and newsworthy.
No, "most interesting" is the superlative form.The comparative form is "more interesting".
comparative : purer superlative : purest
Comparative: older Superlative: oldest
Dative; Early Comparative; Earlier Superlative; Earliest
The comparative and superlativeforms of grand are: Comparative: grander Superlative: grandest
comparative - merrier superlative - merriest
Comparative: shallower Superlative: shallowest
The comparative is "stricter" and the superlative is "strictest".
comparative = sadder superlative = saddest
The comparative is greater and the superlative is greatest.
comparative - rockier superlative - rockiest
Comparative - better Superlative - best