Saturday's campaign, using the HERO System, our GM asked a very interesting question: How do I make it scary when you can hit everything?
Let's add some context. We have the latest chapter of an ongoing campaign with a major horror theme attached to it. Basically, anime-themed supernatural cops versus eldritch abominations. Admittedly, I went a little overboard conceptually, and made a character that was a tad on the broken side in combat. It's ridiculously hard for her to miss a shot. I've been doing my best to try to balance things out, going so far as to create opportunities for the GM to mess with her and not using everything she has at her disposal. Barring that little oversight, though, it is a good question to ask.
To refine the question, I think it's more at 'how do you maintain tension when faced with powerful combatants?' The simplest idea would be that when faced with powerful players, you just bring a bigger gun. In the long run, that just makes it into an arms race and only has a limited effect. A more elegant solution needs to be tailored from whole cloth, I think.
One thing I cannot recommend enough is to pay attention to your players. In order to know what the PCs bring to the table, you must understand their strengths and their weaknesses. Once you have a handle on that, finding ways to exploit those weaknesses should be fairly simple. Not only looking at the stats and numbers but also how the character works thematically and psychologically.
Attacking a weakness seems like an obvious angle to me, assuming you know what that weakness is. Maybe attacking a strength is a good call as well. Disarming a fighter puts some pressure on them. For instance, my character mentioned above is really good in combat, but only as long as she has her pistols. Remove that, and she's not much of a threat.
I feel the trick is to approach from less common angles. Maybe things pop up behind the back lines, targeting the weaker members of the group. Maybe the monsters have a defense against whatever the main damage dealer is throwing. Perhaps the sheer sight of the monster is enough to shock people in their tracks. After all, if you can't beat them physically, beat them mentally. Situational elements also can work. Got a hero in the group? Put some innocent bystanders in the thick of it.
At the end of the day, it's a really good question with no definitive answer. I've just thrown out a number of possible solutions, and none of them are 100% the correct answer. in fact, if the question comes up at all during a campaign, I think the GM should really take the time to come up with as many solutions as they can. Not in the sense that 'my players are min/maxing powergamers' but more as an exercise in 'how can I make everything more interesting?' Cease the opportunity if you can. Questions like these lead to growth in the creative sense. That's the glory of rhetorical questions, I guess. As long as you try to answer them, it doesn't matter if you're right or wrong so much as that you tried.