Nah, it's pretty usual for melee.
Is it also usual for them to be able to slice off 200 or so pts of damage after resists in all elements, on every attack, every round?
Someone posted a randart with over 700 block. That'd be -700 on end damage with eternal guard & spectral shield. More against most attacks (it'd block a 700 physical, 700 lightning hit for instance)
If you're asking if Eternal Guard is overpowered, the answer may be yes. But yes, that's usual for any shield specialist that invests in Eternal Guard-notably, I'm pretty sure you could get that kind of block on anyone you wanted(mages, anyone?).
Generally speaking, though, 200 damage reduction, every round, in exchange for requiring one third of your turns to be devoted to it...even with the Counterstrike bonus to damage, it's pretty balanced. Anything dealing 200 damage was probably not a threat, so it mostly nulls out heavily multi-strike oriented enemies. Then you have to cover the right element(or take a Prodigy, and Prodigies give large benefits in general) with whatever shield you have too.
(I personally prefer to swap shields more than use a Prodigy, though there's obvious benefits to Spectral, namely being guarded by surprise attacks of an element you didn't expect.)
And sure, Counterstrike is a lot of damage added, but you have to be in the range to use it. Keeping that 200 damage barrier up means that you're spending a third of your time not moving towards enemies, and it means you're running an automatic option(or mashing Block every three turns) that you may screw up, leave on at the wrong time, and kill yourself with it.
So no, on base I don't think it's busted. The best shield in the game for block that isn't a randart is Titanic, I believe, at 320-two Prodigies for a 320 damage shaving that takes a third of your turns is really good, but I don't think it's broken. It's a little hard to assess because it's so odd, but...
The reason it may be yes, for me, is randarts and dualblock(Stone Warden). The outlier cases are weird. I've gotten 200~ shields from Randarts, and I've seen 600(700 is a new one on me, that's freakishly rare). 400 isn't all that odd, either, and two 200 shields is still 400 block. It becomes a lot more questionable then. Weird case, and probably means Block just needs some kind of reducing returns or a cap.