Gilmoy: <11.a4> prevents the uglier b5, but cedes the ugly-enough <12..Nb4> outpost.
<15.d5> invites liquidation that could lure the mighty Nb4 away; Black simply ignores it, essentially up a tempo. <15..Bc5> intriguingly accepts ugly doubled pawns, outweighed by long-term half-open b and the obnoxious Nb4-Nd3 tour.
<18.e5> is a 2nd odd pawn thrust: White needs the space, already an admission of Black's clampdown. e5 is overextended, and inevitably could-fall; surely White expected that. Black looks deep-enough, and arranges for it to fall with <piece flow> heading toward White's K -- essentially up +1 more tempo.
<promoted yawn: Could white capture on c4 around move 24 or 25?> 24.bxc4 Qf6 <hidden attack on Ra1 freezes Rd1> 25.Bg2 Rfd8 and Black holds everything, still has a pawn and c4 if he wants it, and even Nb2 tricks.
25.bxc4 Nf4 26.Qf1 f5 looks ugly: Black has a natural attack with Rf6-Rbf8-f4. 27.Bg2 lets Black trade off his Nf4, 27.Bc2?? Nf3+ 28.Kh1 Qh5 <haha> 29.h4 Nxh4+ 30.gxh4 Qxh4+ 31.Kg1 Rf6 and White must return lots of material, hence 27.Bh1 -- but terribly passive.
<26..Ng4 27..Rxb5> is charming: a Philidor! Half-open b pays off in the end.