From my (only) time around the P1 interior, I thought: comfortable, cerebral, cocoon.
For others to be expecting a glitzy & glamorous interior in the same vein as a Pagani offering, Spyker model, etc. but with the mental-manic'like focused performance of the P1 wouldn't be applicable from my viewpoint. The quality of the P1 interior is clearly evident, whether the fit/feel/finish or the ergonomics & layout. Sometimes, just sometimes -> less is more!
One thing is clear, McLaren truly doesn't give a hoot about prideful-yet-insignificant attributes (who cares if it's not a V10/V12 or unique powerplant, who cares if the interior is similar to a 12C, who cares if the CF tub is shared, who cares if it's drama-less, blah-bla-bha...) when it will presumably reset the bar for hypercars in terms of aerodynamics/efficiency/construction AND operability/usability/utility AND performance/prowess/potential.
Serious car. For serious drivers.