He's very strong, but not overpowered. First you have to get Light of Valinor or Asfaloth in your hand to get all these advantages. Then if you compare him to Bifur, he's not much stronger. He has 3 ATT and 3 WP. Bifur also has 3 WP (with Dáin in play) and can easily improve his DEF to 3 (Dúnedain Warning, Ringmail, Arwen). Erebor Boots give him another HP, his starting threat is only 2 above Glorfindel's, and he has an awesome ability while Glorfindel has none. Erebor Record Keeper can ready him when needed etc.
Or take Bilbo - one Dúnedain Warning, Arwen, Fast Hitch and Celebrían's Stone, and he's The Wall. Not to forget Burning Brand.
I like that Glorfindel offers some new deck building options, like Loragorn did before.
Glaurung is right. Glorfindel is stupidly powerful when combined with Asfaloth and Light of Valinor. Sure, you have to start out with LoV in your hand. If you mulligan for the card (and if you are playing Glorfindel, you almost always should), that means you start out with the card about 58% of all games. If you include Runes you increase your odds considerably. In the 40 or so test games I ran with my Glorfindel deck, there were only a couple occasions that I didn’t get the card in play by turn 3.
And a 5 cost hero who quests for 3 without tapping, attacks for three and has 5 health is far superior to Bifur plus any other attachment of your choice. And that’s in comparison to Bifur, one of the most powerful heroes on in the whole game.
Of course Frodo is powerful with 4 or five 5 attachments, but so what? That takes a ton of card draw and resources and he still isn’t as good as Beravor with half as many attachments.
I urge you to run some tests with the new Glorfindel. Use my deck, use one of Glarung’s decks. GLorfindel and his attachments are game breaking. Now, as Valyrian Steel said, that may not be a bad thing, but we shouldn’t be disputing the power level of this combination of cards. It’s off the charts.