Kizumonogatari Trilogy is chronologically the First entry in the series, but Monogatari series is meant to be watched / read in non-chronological release order. So technically Kizumonogatari is the second season in the series overall, it CAN be enjoyed as a standalone / entry point (in my opinion). Though a lot of fans will say otherwise, and it might create some minor confusion, but I 100% think that it can be enjoyed without watching other seasons.

As the above person said, kizu trilogy can also be enjoyed as a standalone without watching bakemonogatari since it doesn't spoil anything being the first in chronology