For once, the villain just shoots him.
Make your villains in games do this. No player will ever expect it.
Commentary by memnarch (who has not seen the movie)
...... Okay then. What's the catch? We've had all of this build up, Corey even said he didn't take stupid risks, and here's Luke getting blown up without doing anything. Mind you, the blast at his legs looks really weird, but there's been a few still frames that look kind of odd before. So..... Force Power Shield? Not impossible I would say; I'd already thought that Luke would be able to do something to block blaster shots, but I'd been envisioning a mass of troopers firing rather than the AT-ATs.
Oh, and the helmet definitely helped Kylo, I have to say. Even after finding out that he's just a Darth Vader look-a-like with that as the most likely reason he had a helmet, there's just something intrinsically menacing about an unmoving blank face. Plus, you can't have your mouth just hanging open with a stupid look on while wearing a helmet like that.
Transcript
Kylo Ren: All units! Fire on him!
General Hux: You’re not going to go down and take him on mano a mano?
Kylo Ren: Do I look like an idiot?
General Hux: Hard to say whether removing the helmet helped or not.
General Hux: Anyway, are you sure shooting him is wise? What if he deflects it back with his laser sword?
Kylo Ren: Don’t be ridiculous.
General Hux: It’s literally what Jedi do.
Kylo Ren: Blaster bolts, sure. But these are heavy artillery.
General Hux: Yeeesss... And if one bounces back towards this shuttle?
{beat, Luke stares defiantly at the command shuttle}
Kylo Ren: Aim at his feet!
General Hux: Hmm. Let’s hope he’s never played space hockey.
[SFX]: Pow! {a walker fires at Luke’s feet}
[SFX]: Ka-Boom!! {a huge explosion sprays red mineral dust into a tower many times taller than Luke, where he was standing}