I think that this ability is a bit overpowered in that it does good damage, has a large AoE, good range and a relatively short cool down. Armies with moderately heavy, short range infantry with large squads get massacred by this ability, SM in particular, I don't want to see poor BS face this. Heavier infantry like Terminators will basically take the full damage because they don't get knocked very far.
In a game today, I was attacking the Tau's base and it looked like I had the upper hand, I was about to pull my missile squad up to start attack the barracks, but it along with its apothecary was no where to be found, only large craters in the place where I last remembered them to me. This basically cost me the game, but it was a good one still.
I realize Skyrays are probably one of the best examples of a glass cannon, but I think it should be less "kill it within 4 seconds or its GG" and more "o noes! better get my AV squad up here". I think it's overall range should be slightly nerferd along with Missile Barages range, but it be given more hp (right now 1 melta will leave it with about 150hp).
So buff its hp a bit, but reduce its range or something .