Giddens has many interesting ideas and certainly one can endorse his rejection of "market socialism."
One suspects, though, that he places the "Third Way" too far to the Left. In particular, his emphasis on anti-traditionalist transformation in the area of gender and his appeal to Habermas are suspect. Habermas is not "Third Way"; Habermas is the extreme Left. So is most of what passes for "feminism" today.
I think the major idea between the "Third Way" term is that earlier Leftist politics need to be limited, even as the militaristic Right needs to be rejected and even as broader non-acceptance (in something of a libertarian mold) of "conservative" thought on social issues needs to be maintained. There is then much dithering on how far socialism needs to be curtailed at the moment, and on much disagreement on social issues such as abortion, school prayer, etc. (although no major "Third Way" thinker today consistently and ardently take the "conservative" side of these issues).
There is also a generally taken-for-granted rejection of what we might term "strict libertarianism": the view that, in almost all cases, the option of immediately moving toward limiting the government's to protection of property rights is the better option. This type of libertarianism just isn't on the radar for most, but I think it is fairly evident that the Third Way is not compatible with this libertarian option (an attractive one, in many ways, at least as compared to the type of government we typically get in the U.S.).
One might distinguish between "Left Third Way" and "Right Third Way." Left Third Way wants to disguise its socialism under new colors, the better to sell it. It's not so much that socialism failed, as that the public gagged on it. Right Third Way honestly doesn't want substantial, long-term increases in the percentage of GDP devoted to government, but it does want the massive amount of wealth the government takes in to be well-spent and procured progressively.