Let's look at what Luke has actually managed to do with the power of the Force, on-screen.  

Episode IV

- Blocking a toy dueling droid from hitting him with non-lethal lasers while blind
- Timing perfectly a pre-programmed photon torpedo to barrel down a thermal exhaust port

Episode V

- Tug a lightsaber out of snow
- Have a very vague vision of disaster (that lost him an arm)
- Jump like Michael Jackson out of the Carbonite Pit
- Connect with his sister's latent force sensitivity by shouting

Episode VI

- Get a bunch of weak-minded lackeys to almost turn on Jabba before getting awoken.
- Catch a lightsaber in midair like um....a good Football Player?
- Tell that he shouldn't have been on the mission because of Vader
- Levitate C3P0 on a chair

Impressive...but only if you don't compare it to any of the incredible things done in the Clone Wars cartoon or the Trilogy.  And, as pointed out, his lightsaber work is pretty weak.

All of this indicates that Luke's skill level is pretty dang low, despite having great potential, due to a severe lack of training.  He did 'defeat' Vader, but it was through sheer aggression, and in the end was more a psychological victory.  

In short, Luke's actually not that good compared to the Jedi Knights of Old.