Unlike with the Dark Eldar and Grey Knights where shooting them was sufficient, that does not work against the Necrons. Quantum Shielding makes all of their vehicles essentially AV13 until you get your first penetrating hit against them. That is heavy armor. Not exactly easy to penetrate, even with Lascannons and/or Tank-Hunting Missile Launchers. Add to that, all Necron vehicles have Living Metal, which pretty much negates Crew Shaken/Stunned results unless your opponent is unlucky. Bad news.
On top of that, the new "We'll Be Back" (now named Reanimation Protocols) is a 5+ roll after EVERY phase where the Necrons take casualties. Against every type of wound possible, including power weapons, instant death weaponry, and AP 1/2 stuff. The only way to negate the Protocols is to kill the unit outright via shooting, CC, Sweeping Advance, or some other ability. Also bad news.
Next up, all of the Necron stuff that is CC-oriented is tough as nails and hit extremely hard. They are either rocking T5, invulnerable saves, or both. Even when faced with I2, they will survive nearly intact to fight back. And they will kill stuff. Pretty much everything hits at high strength (5-7) and is using power weapons or rending weapons. After its said and done, its very unlikely they'll lose combat by much, if at all. This leaves Sweeping Advance largely irrelevant against everything but the weak Troops that even the Necron player doesn't really care about (because they are dirt cheap now).
The Stormlord is a game changer. He can seize the initiative on a 4+, can make multiple turns Night Fighting (potentially 5 turns total), and is no slouch in CC. The Necrons also have Fast Skimmers now, making them incredibly mobile if they so desire.
And most importantly, they have AMAZING shooting capabilities now. Most of the good stuff is 24" range, but there are quite a few weapons that you'll be seeing a lot of that are long range. Such as the Doomsday Cannon (on Doomsday Ark), which is a MEQ killer. It has two profiles, but the big one is a 72" Str 9 AP 1, Heavy 1 Large Blast. This thing is a practically a demolisher cannon that doubles as reliable anti-tank! Yikes! The Necrons also have melta now (with two shots at 24"), which is found on their new walker: the Triarch Stalker. To cap it off, torrent of fire with high powered weaponry is definitely found in multiple units in the codex. This codex is extremely balanced.
But not all is lost. The Necron codex is very "elite". The real dangerous units are appropriately priced, so its not like you're going to see lots of the hard hitting things without sacrificing things elsewhere. Plus, their stuff is mostly mid-range. So, providing Stormlord isn't on the board, you might be able to take them out before they get into range. Maybe.
Moral of the story: I'm not screaming doomsday for the Black Templars. But we're definitely going to have to adapt, yet again, to stay ahead of the curve. I won't lie to you, Necrons just might be harder to beat than any other codex for us right now. Its going to take some time to analyze and dissect the new codex, so that we can find ways to beat them. Have patience, we'll build something that is effective against the Necrons AND all of the other codices. Though, I'll admit, this new codex makes me want to built my Defensive Drop Pod list even more. ;)