I have to admit that I was initially frightened by the "threat changes," but now I think I'm excited to play my main Guardian. The only problem I have now is which two trees to pick...hmmm...
It looks like all Guardian builds will need a decent amount of crit, seeing all the "does x on a critical hit" on skills, especially the self-heals. I hope we get gear with more crit and/or Fate, as it's not a stat traditionally part of tank builds. Also, I hope non-FoS builds are pretty power-efficient if we're all but losing Thrill of Danger...or else the Tireless Defender/Guardian's Ward combo will become very important (note its accessibility). I have to say I've only noticed power problems in dungeons with power-draining diseases (e.g. GB--don't recall which one), but power restoration is still quite nice to have.
catch a breath now restores power after a parry and morale after a block as a baseline function of the skill. there is also a new legacy that increases the power heal (in addition to the current cooldown reduction and morale heal boost legacies)
yes, crit will be important for everything. in yellow, at least, you'll get a stacking crit buff whenever you parry and in blue line, there's a +5% crit boost from shield spikes (that also increases the duration by 10m)
One thing I don't like about the current system is switching off between sword-and-board and a two-handed weapon. It's difficult to maintain two completely different LI's (or pairs of LI's, if you count the belt) for two completely separate purposes (tanking and DPS/leveling). If the Fighter of Shadow makes it possible to tank with a two-handed weapon, will shields be cast aside in favor of great swords and great axes? Or will the FoS line be restricted to off-tanking and DotF be the only true main tanking line? Players wiser than I should answer these questions.
you can still tank with a shield in yellow line. the difference is of course the stats of the shield versus the damage and threat of a 2h as well as having access to the shield skills: shield-blow, shield-swipe, and bash. shield-taunt is blue line only, and it is possible to pick up shield-smash, but probably not worth it for yellow line as it requires a lot of offspec point investment.