I would say that HS2 management has broadly managed within the directions provided. That has generally involved being willing to add billions to the design cost rather than offend the Woodland Trust or residents of the Chilterns, attempting to deliver to a timetable which wasn't manageable from the start, and not sufficiently altering this to address the realities of the post-Brexit construction industry.
Whilst the additional tunneling in the chilterns increased the cost of the scheme, some of the additional tunneling imposed on HS2 is projected to have reduced scheme costs.
See the original plan to demolish and rebuild Hangar Lane Gyratory to avoid a tunnel out of London - which better cost estimates demonstrated dwarfed the supposed savings from avoiding tunnels.
In any case, extra tunnels are unlikely to represent a dominant portion of the cost growth that HS2 has seen.
There was very little opportunity for HS2 management to do anything about any of the things which increased costs - they basically all came from politicians as the cost of the barely-maintained consensus.
To cite just two, HS2 management decided to launch an unwinnable attempt to force the rewriting of the Technical Standards of Interoperability to meet HS2's desires.
We also have a lot of disturbing stories coming out of the company that have been extensively reported in the press, which may or may not be substantiated.
Nevertheless, neither of these things is a good sign in the slightest.
Personally, I think this scheme was probably doomed from the start, but the management have hardly covered themselves in glory on the road to here.
It certainly does not convince me, or apparently the new government, that giving HS2 more money to try and get more built is a particularly good idea.
The way things are going we will probably get a rebuild of Euston that include high speed platforms, but even that seems far from certain.
Asking for anything more than the bare minimum at the north end is almost certainly an exercise in futility.
The fifteen kilometres to Hixon would give us a high speed rail line that can at least approach its capacity capability, assuming some kind of station is built at Euston.
I think that that is ultimately the best the railway can hope for.