I enjoy exploring the worlds and reading the lore. I love the idea of having a codex / encyclopedia galactica / hitchikers guide to the galaxy, but I find it extremely frustrating that it can't be completed / unlocked completely.
Map Exploration Frustration
Mountains and un-traversable terrain shows up as empty hexagons until the entire area has been explored. I like to try to unlock the entire map, but when these things exist, its not obvious which parts are unexplored, and which parts are simply unreachable. If the area is simply unreachable, then it should be revealed with one of the adjacent areas - not with finding the last discoverable area. Exhaustion zones are not indicated on the map there should be a planet achievement for unlocking the entire map
Codex Frustrations
There are too many bugged codex entries (see this thread: http://www.swtor.com/community/showthread.php?t=104803). Before I came to this realization, I tried to find everything on the first few planets, and just ended up wasting time.
Its not always clear how to unlock something. Do i need to complete a quest? Choose the right dialog in a conversation? bestiary discovery seems arbitrary. Sometimes its the first time you see one of those species. Sometimes it seems like you have to kill a certain amount, or kill one in a certain area, or maybe you need to kill one of each variation of that species, or a specific elite version. So far, I don't see a pattern. Sometimes, no matter how many you kill, click on, run past, you never "discover" the beast. Some datacrons listed in 1 planet's achievement, are physically located on another
Suggestions
modify the codex to have be checklist for all the specific things in each category (notable people, beastiary, species, etc...). The guide might not reveal the exact locations of datacrons and the world boss, but it should give general clues / hints (and include region / sub-region) on how to achieve each goal. If it requires a quest chain to unlock it, indicate who the quest giver is in the clue, and there should be no level cap on starting the quest. Instead of making this the default behavior, maybe there could be a tourism vendor on each planet that sells a "tourist guide" that contains hints on the planet's codex entries (e.g. unlocks the checklist) a tourism vendor could also sell special items to individuals who have explored most / all the planet has to offer (maybe food that is slightly better than the cantina food make a legacy codex, so that one legacy could unlock the entire codex - including both faction and class specific lore. Each character would have its own codex, but the legacy would track the aggregate of all characters.