What i'm hoping for is mass customization of one's character and ship. I'll be pretty dissapointed if every hull you purchase is the same as everyone else. Being able to choose/upgrade your ship's weapons, armour, speed, etc would(will?) be great.
Customising characters: yes
Customising companion characters: yes (not their sex, race or body type though). You will even be able to change their AI at launch.
Upgrading ship weapons and equipment: yes
Having a ship that looks different to other ships of the same type: no
You won't be able to change the way a ship looks, nor in fact be able to choose your ship in-game (although it is free and part of the storyline). Each class has a specific ship which it gets, and that ship cannot be visually altered on the outside. Although this seems like a stupid limitation I believe it is because the ships are in pre-rendered videos which are played at points in the game, and to allow visual customisation would mean that either your ship would look different to the way it does in the video, or you'd have to have tons of videos downloaded each with a different variant of the ship doing the same fly-by (which is obviously unreasonable to expect). To be honest I don't mind - I loved ship customisations in SWG, and I like how you can have different looking ships in EVE of the same hull, however I do understand why Bioware have this limitation in place (to be honest the KOTOR and Mass Effect series don't let you change the look of your ship). Of course all space content at the moment is single player so you won't see swarms of player ships all looking the same fighting in a massive battle, hopefully when they release multiplayer space content there may be more options for making a distinctive ship.
The real strength of the game will come from the stories, and the fact that it isn't a race to max level - unlike games which have grind phases of just killing the same things over and over to level so you can reach max level and hit end-game content, SW:TOR is about your character and their companions' journeys. It is less about the destination and more about the journey. That doesn't mean there is no end-game content - in fact there is end game content for people who like raids, people who like pvp, people who like small group content and solo gamers - so there is something for everyone.
