I'm still currently subbed to swtor, have 3 level 50-55's on Jedi Covenant and a handful of lower levels. I reupped my sub after a year to play the new galactic starfighter expansion.
When i first started playing the game, it was with a group of arfcommers, and it was right after the game went free to play. We all pretty much lasted 1 day before we were all subbed...its night and day.
#1 F2P you dont start the game with the faster run option right at the start at level 1. You can unlock it later i believe as a skill, level 12? 15? something like that.
#2 You can't learn your first speeder training level until a later level.
#3 You can't equip purple's (the highest rated gear and mods in the game) Found this out by taking my 50 and soloing lower level world bosses for the gear drops to give to a clanmate who was free to play.
#4 You can only have so much in game money at one time. Once you hit your cap it starts banking your extra cash that you can access if you ever upgrade to preferred or sub. This will also make it impossible to buy higher priced items in the auction house.
#5 You cannot PVP warzone, do space missions, etc without buying passes. this will be either through the auction house with ingame money or cartel coins via cartel market (real money microtransaction shop)
#6 You are limited on how many crafting/gathering/ crew skill you have (think you can only have 1 or 2, where as subs get all 3)
theres probably a bunch of other things i'm missing since its been awhile since i've had to deal with the free to play stuff.
Dont get me wrong tho. swtor is an awesome MMO, it was one of the first ones i played i thoroughly enjoyed. The game has great stories and so many cut scenes and dialogue that some MMOs just dont have.
right now tho i'm also subbed in elder scrolls online