So says this report, but there's a few things that draw my eye.
1) The information was provided to Trump. It's not being held as a weapon to use against him in the last few days before he takes office. It's a warning, perhaps, of vulnerabilities he doesn't know he has; or it's a play at leverage from an intelligence community that would like to be closer to their new boss. (Don't think a clandestine service guy wouldn't think of this. If he didn't at least think of it, he's not competent at his trade.)
2) The information was provided to Obama. He's giving a farewell address tonight, not girding his loins up to do something unprecedented. That suggests that the information we're seeing in the press should be interpreted minimally rather than extravagantly.
3) Nevertheless, this is a big deal if true. It's not a crime to be the victim of spying (otherwise, we'd have yet another reason to put Hillary in the dock). There are crimes that can come from how you respond to being blackmailed. Right now, we don't know enough to know if any such things happened. Indeed, Trump may not have been at all blackmailed as yet: he may have been surprised to learn the information existed.
There's a lot to know yet before we can come to any conclusions. It's not even certain if any of this is true. All the same, it's something to keep an eye on. Even if it turns out that Trump just took a bunch of easy money from Russian outlets, it's not too far a walk to bribery -- and bribery is one of the two Constitutionally specified impeachable offenses. If you get as far as treason, well, that's a capital crime.
Strange place to start a new administration, and again, what we have in front of us is a leaked comment about a report that the President has seen in full and isn't taking super-seriously. Still, a citizen's duty is what it is. All partisanship aside, we'll have to keep our eyes open and do what duty and the Constitution commands. It may come to nothing, but we cannot be sure it will.
UPDATE: NBC says the intel agencies didn't show the 'compromising material' stuff to Trump, because they deemed it false. That's odd, though, because Trump sounded at his presser like he thought he had seen it. (Quite a presser, too -- it's going to be an interesting administration.)