A very interesting level pack for Doom that mixes fascinating challenges like narrow platforming, hidden eye switches, and disorienting mazes to freshen up Doom's mechanical appeal somewhat. Sigil is short and fast-paced, staying just long enough not to bore, but it does objectively feel like EXACTLY what it says on the tin...more Doom levels. And if you've played through the main campaigns even once, these levels won't shock you like some other popular mods might. All in all, a good use of two hours or so.