A few things I've noticed so far, nothing conclusive from my end either;
PVP - My biggest grip with PVP is that it appears anyone from level 10 orwhateverisminimumlvlforpvp to max level of 50 can end up in the same battle. There is no segregation of levels like it was in WoW, 10-15, 15-20 etc etc. That balance things out a bit and makes it harder to get entierly overwhelmed by a completely superior character.
The 'fix' to this is to boost a toon's stats to the level of the highest level enemy player. A lvl 42 Sith Warrior enters, my lvl 12 Jedi Sentinel get's boosted from 1884 HP to 12546 HP's. That compensates, right? No it don't. I've barely started on the Sentinel path, at level 12 my skills are few and low compared to the 42 level Sith with his way more and far more powerful abilities - his crowd control nearly allways hits, if his don't his friend's ability will. All my attacks hit a wall of higher resists and cutting into a 30-40 something foe is CONSIDERABLY different from attacking a level 14 or so enemy who's barely over my level.
Let's not even start on the difference in gear and equipment.
Second part is the idea of the 'wow-clone'. It's undeniable that many aspects of WoW's gameplay is to be found in TOR, mostly this is for the better however. I see so much of WoW's gameplay that worked in use here, and this lends a flavor of old familarity to the game. (This will be good or bad depending on who is asked.) On the other hand much of what blew up in WoW's face is noticably lacking. Item level, Achievement whoring, rampant pet collection, auto-instance/raid finder across servers etc.
Most if not all the factors that eventually degraded wow into what it is now seem to be lacking.
Lastly is the duality of the 'alignment' system - it's possible to get gear based on it - in fact if you go light you get a good selection of light side exclusive gear and vice versa. I don't know if any of the gear available from one is superior to the other but I do know that if you go for one your denied the other. There is no middle ground so this force you to aim for A or B, to much fidling get's to conflicting score and in mid-to-end-game it seems you need high score one way or another to get access to some of the best gear. Trying to follow a borderline toon or one with a specific viewpoint (say, a rough trooper who is merciless, cold and effective (much dark points) but humane and caring to his/her cause and faction (more light points)) can easily land you to few of either points to have access to hig-end stuff denying you high-end gear. This hurts immersion, among other things, especially as some of the choices asks you to be either stupidly naive or nice or needlessly cruel or in-humane for the hell of it.
As an example, I'vetaken my trooper to level 11 so far, got off the origin world and so on, and some of the choices made simply did not make sense - this person's record, if I had gone 100% goody-goody for instance, would include a number of order-violations and out-right unacceptable stupidity. Only dark options were not much better.
*edited to fix typos and add some to the end*