Is the Blaster Launcher worth the time required to obtain it?
My team is all geared out with full plasma weapons, psi armor, and ghost armor. My Gallop Chamber is built and I'm ready to go... but I haven't seen any battleships and therefore haven't had a chance to research and acquire a Blaster Launcher. I understand that you can sometimes trigger a Battleship by letting a detected UFO go unharmed, but what if the Fusion Core I need is damaged? And then what of the time spent researching?
Is the Blaster Launcher worth all this trouble or should I just go for the endgame and keep my eyes peeled for battleships in future games? For the purposes of answering this question, I am uninterested in novelty and speaking strictly about whether or not the weapon imparts a significant battle advantage.
Solution 1:
The Blaster Launcher is a phenomenal weapon, it instantly transforms the most dangerous enemies in its range into relatively safe encounters. Let's see what a heavy with Danger Zone, HEAT ammo and Rocketeer can do, and remember, the Blaster Launcher always hits:
Groups of elite mutons - take the lot of them down from 14 health, enough to survive anything except a plasma weapon critical or a plasma/alloy rapid fire, to 5 health, easily killed with any plasma weapon or Mindfray. If your other operatives have a good chance to hit, you can kill them all before they even get a turn.
Sectopods - deal 18 damage and kill both support drones, leaving it with only 12 health. This means you only need 2-4 operatives to use their turns to kill it, freeing the rest to deal with other threats.
Cyberdisks - instant death.
Groups of chryssalids - instant death.
Ethereals - 9 points of damage out of a total 20 with no chance to reflect. You haven't felt pain if you haven't had a plasma bullet swarm reflected at your heavy. A solid opener or a lifesaver if it's your last move. Very likely to inflict grievous harm on the Ethereal's buddies.
The final confrontation - guaranteed win in the first round with 3 blasts, and the 3 spare rockets from Rocketeer mean you can dominate the opposition leading up to it.
I believe taking Mayhem instead of Rocketeer will let you kill most enemies outright, including Sectopods if you have HEAT ammo, but the extra rocket is too good to pass up, in my opinion.
Now, for the most important feature of the Blaster Launcher - the projectile will route around obstacles and even break windows to reach its target, this means you can place the devastating explosion exactly where you want it, instead of only where your heavy has line of sight. This feature instantly transforms your heavy's secondary from something you use every now and again because it's almost impossible to get a good shot into a major staple of your tactics.
The transition from Rocket Launcher to Blaster Launcher is the single most important weapon upgrade an operative can get, comparable to going from regular weapons to plasma weapons. Can you complete the game without it? Sure, though the Blaster Launcher can guarantee a win, while most other weapons only give you a fighting chance. Is it worth delaying the final mission to get it? Doing so will expose your operatives to quite a few dangers, so it may be prudent not to risk them if you do not have replacements, but clearing a Battleship is a nice achievement in itself and the prize is worth the risk if you have replacements.
Solution 2:
The Blaster Launcher is certainly useful - in a few situations - but IMHO it isn't worth delaying the final mission for. The chance of it saving your squaddies is probably less than the chance of a mission going bad while you wait and some of them dying that way.
It does offer higher damage, but so long as your heavies have HEAT ammo and Mayhem, there aren't many enemies that can stand up to a normal rocket anyway. Muton Elites perhaps. That just leaves the shooting-round-corners aspect, and I don't think I've used the thing enough to have an opinion on that.
The Slingshot DLC does allow the player to get a Fusion Core much earlier, and (speculating) it may be that the development team did not intend in the first place that many games would be completed without the player ever getting one.
EDIT: The other feature of the blaster launcher is that it's a guided projectile rather than a straight-line shot. When fired, the UI becomes similar to a move order for a flying unit, and the blast projectile will follow the path before detonating at the indicated designation. This includes going around corners and obstacles, and only requires that the terrain has been visible at least once during the mission.