Essentially, Orisa becomes a walking Winston bubble with a few caveats.
Enemies can walk through it, but no enemy bullets/projectiles can penetrate it or break it. It's an invulnerable shield that lasts as long as her normal ult, and I personally like the idea. It's a unique concept that hasn't been done yet, and adds a type of support ult to the Overwatch pool.
The ult could be great for protecting a Symmetra going to put up a clutch teleporter, shielding McCree while he charges his Deadeye, or securing the payload the last few meters. It's a creative idea that could help Orisa stay relevant in the wake of these changes to Mercy, and keeping heroes relevant is tantamount to Overwatch's success.