The budget cuts always seemed pretty apparent to me. There's only a single episode that went out on location ("The Paradise Syndrome"). There's tricks to avoid using new special effects or build new models (The Romulans using Klingon ships in "The Enterprise Incident;" the invisible ship in "Let that Be Your Last Battlefield"). There's the over-use of ship-based episodes (the exact duplicate of the Enterprise in "Wink of an Eye" is one of the laziest excuses to re-use standing sets ever). There's more tracked music, and fewer original scores.
Bob Justman wasn't off by much when he called the third season "a radio show."
Bob Justman wasn't off by much when he called the third season "a radio show."