The Rocket Launcher costs 4 effective resources to play (3 plus the card itself). Champions cards are usually judged to the standard of 2 damage per effective resource. By that standard, you are meeting expectations if you can use it against the villain plus one minion, twice.

However, it is important to note that the Rocket Launcher, like most of Rocket's tech upgrades, does not have the "uses" keyword. This means it stays in play after the last charge counter has been removed and is a valid target for Rocket's "Tinkering" ability, providing a 2-resource rebate. This possibility makes it more efficient than it seems at first glance.

I don't think you're ever going to be upset you played the Rocket Launcher, but if you draw it and the Particle Cannon in the same turn, judge what you play based on the number of minions you expect to encounter.