I really like the endgame group PvE in The Old Republic. As Goldilocks says, "it's just right" for me. In fact, in a lot of ways, I would say that it feels even better than the current incarnation of WoW group PvE.
I think the biggest thing is that TOR has the balance between AoE and single-target almost perfectly correct. Sometimes you AoE, and sometimes you single-target individual mobs. Crowd Control is often used, but it is not absolutely required.
In contrast, WoW has devolved into spamming AoE much of the time, especially in 5-mans.
I think one key element is that AoE in TOR tends to be either much weaker, or on a long-ish cooldown. For example, my sniper has one excellent AoE, Orbital Strike, but it is on a 45 second cooldown. So you can really only use it every other pull, or once every three pulls if you're moving quickly. The other two AoE abilities are very weak compared to the single target abilities.
The other major key is probably the composition of trash packs. Trash packs are often composed of several mobs of differing strengths. There are weak, normal, strong, elite and champion mobs. AoE is really only good for dispatching weak and normal mobs. The other types take too long to kill with AoE.
As well, the tank really only needs to tank the elite and champion mobs. Strong and below are roughly what you encounter in questing, so the DPS can take them out with only a little healing.
So in TOR, a standard pack often sees one of the champion mobs be crowd controlled, the tank jumps in and grabs the elite or other champion, and the DPS start single-targeting the other adds from weakest to strongest before moving onto the tank's mobs. This gives the tank a fair bit of time to build threat, and keeps threat reasonably important.
Or if there's many weaker guys, AoE is used to clear them out while the tank holds the stronger ones, and the stronger ones are finished off with single-target abilities.
Another factor that might contribute is that there is only 2 DPS in a small group in TOR. They can't bring a huge amount of AoE damage to bear. You would think that this would make DPS waits very long, but oddly, I find that they're about the same as WoW, about 15 minutes or so.
It's so much more fun than the current WoW 5-man instances, where the tank grabs everything in the group, and the three DPS start AoE'ing. Meanwhile the tank has super threat, and can't be pulled off. Indeed, actually single-targeting things makes it more likely you will pull threat.