If you mean gameplay wise, we can’t really be sure until KCD 2 comes out. It’s not impossible that some players would end up preferring the final balance of KCD 1’s gameplay to KCD 2’s gameplay. Plot wise, there will certainly be one or two big plot twists from KCD 1 that will be spoiled if you start in KCD 2.
https://www.reddit.com/r/kingdomcome/comments/1crl39m/must_i_play_kcd_before_kcd_2/