The single biggest reason why I dislike Boomerang (among many reasons to dislike it) is that it breaks Crim design philosophy. Crims, you see, are Criminals (big shocker there). Their stated goal for why they run is money and their most prominent cards embody this. Paragon (and its more broken predecessor, Desperado) pay you for running. Inside Job and Spear Phishing show how Crims prefer to evade their problems rather than waste money confronting them. Finally, Crims are, well, criminals. They steal stuff. They are especially good at punching Corps in the nose and keeping them down.
Crims however don't confront stuff all that well. They're not really supposed to, you see. Their Fracters are either good but conditional, okay, or laughably bad and outdated (meaning they are in real danger of being locked out) and their Decoders are either great but expensive or just okay. Crims splurge on Killers but only because it's the breaker type that prevents their toys from breaking the most. All this, of course, ignores Aumakua, but even that anomaly is run-dependent and thus somewhat forgiven. Simply put, Crims, more than any other faction, do not wish to overstay their welcome.
Crims lack longevity, basically. That's reinforced by their pick of the color chart as well. They're supposed to be the faction with powerful Events and Resources but little in-faction recursion, and the wisdom of that design decision really shows in Boomerang. Boomerang's self-recursion ability propels it from good to just plain obnoxious. Crims are the Runner faction that emphasize the early game, with a playstyle defined by tempo, control, and resource denial. Crims are supposed to hit fast and hard, getting away with anything, but needing help to reach their goals honestly.
Boomerang breaks that mold entirely. Its recursion is infinite, allowing for cheap, endless, strength-ignoring breaking, fodder for endless installs, and its trash ability allows for endless profits. Boomerang on its own defines Crim endgame strategy in that the Crim endgame is simply 'infinite Boomerangs.' 'Infinite Boomerangs' is, in fact, so good and reliable an endgame strategy that other factions import it in. The faction that's supposed to have the weakest endgame is now having their endgame strategy imported by other factions...
Let's hope that easy, infinite self-recursion isn't something pursued in the future. We already have two cards like that, both of them in Crim. One of them is Boomerang and the other one is banned. Note that the banned card has much more stringent recursion conditions than Boomerang.
Well, there are things that prevent (in different levels of mastering the game) that makes boomerang less hard— valerian32
I mean, you can (as a runner) choose a bad ice that it's not going to be rezzed. As a corp you have not many, but there are other ways to prevent the run to end successfully. (Border control, crisum grid) Also the multi sub ice is more common nowadays so you can get only 2 subrutines out. Also you can't have more than 1 boomerang on the table.— valerian32
Aside from the fact that all of the ways you mentioned to make Boomerang 'less hard' are reliant on the runner with minimal room for reaction from the Corp (BC and Crisium Grid have to be installed beforehand), my main issue has always been that Boomerang adds a specific powerful effect to a faction that lacked those particular effects for good reason.— KoRayven