For surface missions, you are accompanied by Mr. Spock and Dr. McCoy, of course and sometimes a security officer (aka Red Shirt). Sometimes you also get other crew members in your party, like Scotty or Chekhov. There are plenty of puzzles for each mission, different times to collect as well as different outcomes depending on what you do. Being reckless or not being diplomatic will affect your score, thus affecting whether or not you progress through the game.
You will also be able to pilot the Enterprise in battle, and when flying to where ever you're needed. FYI, they took the basic control sequence and applied it to the Super Nintendo Game, Starfleet Academy. If you go off course, different things happen as well.
Everyone from the series offers their voice here. Sometimes there's a little too much dialogue and listening too much of it can make a person bored. They tried to recreate it with The Next Generation crew in "A Final Unity" but that game was kind of on the dull side. This game sticks to everything from the original series, and is really a good adventure game. You'll enjoy it a lot more if you're a fan of TOS.