I ran in multiple pairs of all the 2100s series and liked them all (ok I loved the 2120s) the 2000s surpass the 2100 series.

Lighter, better feel, great fit, great balance of cushioning.

I was a bit worried about fit after reading some of the other reviews but found them to be true to size - no problems in the toe box or heel area.

I can't emphasise enough how comfortable these shoes are to run in. Tempted to stock up in case the next model is inferior.