Being able to tank effectively is about controlling the opponents. That is rather difficult to do if you cannot see who your opponent has selected. Especially with the design choices of The Old Republic throwing multiple opponents at you at once. There is very rarely an instance in which you will be fighting with a single enemy, and in order for a tank to accurately control threat and keep the damage coming his way, he needs to be able to see who is attacking him and who is attacking someone else.
Bioware has introduced quite a robust companion system in The Old Republic that makes me want as many companions as possible. The only issue is, with their fantastic built in crafting system, you send your companions off to complete objectives. While they are away on crafting missions, you cannot look at what armor and weapons they currently have equipped. This is quite frustrating when you are trying to complete a quest and companion specific armor is presented as a potential reward, yet you cannot pull up their equipment to compare the stats of the items. Instead you have to wait until they have completed their crafting mission, which can be quite long especially at later levels, and return, then you have to summon them and then have to re-open your quest through the awesome 'pending' system for quest rewards and discover that the item they already have is better than the reward. It is quite cumbersome, especially when you could just have a companion screen built in to show all of your companions and their equipment.
I bought a copy of The Old Republic for my brother so we could play together, but he had never played an MMO before. The tutorials are lackluster and very basic. While they do work, every once in a while I would have to explain to him in further detail what the tutorial couldn't. Most tutorials are only a few sentences, and while that works for something like explaining movement, explaining a skill tree and an entire crafting system via two to three sentences is vague at best to the MMO newcomer.
At level 10 you get to pick an 'advanced class' in which your starting class gets broken into two archetypes with three different skill trees. While I understand this from a design point, locking you into an archetype permanently without anyway to undo your situation short of re-rolling the same class and then playing through the same starting zone again at level 10 is a bit short sighted. It is a leap of blind faith, as the descriptions of each specialization is short and you don't really get a feel for how one advanced class plays against the other you could have chosen. I would recommend at anytime between 10 and 15 you could experiment with each of the two advanced classes, and then at 15 you would have to make your choice permanent.
While I am sure I will have more qualms as I push into the final twenty levels of character progression, these are the immediate issues that I think need more work. I can say for sure because of the immense amount of story content that these minor issues will not keep me from playing, but they could be improved upon to make for a better end user experience.