I don't see how this just isn't flat-out better than the fighter at being a defender. You auto-mark everyone adjacent. You get the same interrupt when a marked foe attacks someone that's not you - except that you target Fort instead of AC, and give everyone CA vs the enemy. Or you can pin them down out to a range of 5 (I'm guessing you can't do both). Plus, you get 2 saves every round (possibly avoiding negative conditions flat-out) and have more hit points. As mentioned previously, the AC is a wash due to Guardian Might.
The power creep keeps on creeping on...
Actually, I do not agree. Fighters can... and often do in my games, mark at range. The warden can ONLY mark you if your adjacent. If you then run away he can pull you back in (I like that he seems like a writhing clump of roots and bark).
Wardens do not come close to being strikers, I've seen fighters and even strength based paladins get into the 20's routinely with their encounter powers, I see the warden having to be built specifically to do so.
The warden gets a "stance-like" effect with his dailies but at the cost of 1-2 W in damage or the ability to be reliable.
I like both but do not yet see the warden as better all together.