Even though the unofficial fifth episode of Doom was supposed to launch in February, John Romero decided that Sigil won't be launching until April 2019, as he wants everything to be 'top notch for fans' who bought the special editions.
Romero wrote that "there were a few snags in production" while ensuring that the packages are quality stuff, referring to Sigil's Big Box and Beast Box special editions.
Even though Romero's wording makes us think that the actual work on the gaming part of Sigil is finished, the actual launch will have to wait until Big Box and Beast Box packages are shipped sometime in April 2019.
Sigil itself will be free for anyone to download, although you'll have to own the original version of Doom from 1993 to run it. It packs nine brand new singleplayer and nine deathmatch levels, built of course by Romero himself.
Big Box and Beast Box editions come with music by shred-legend Buckethead, with a tune made especially for Sigil, and works by another metal icon but on the visual side of things - Christopher Lovell, whose cover art you can see on both of the images here.
The game actually ships as a megawad, which is one huge WAD file, or WAD to rule all WADs if you will. Younger users may not be familiar with the format, but it's actually a pretty funny story - it stands for "Where's All the Data?".
It was John Carmack's pretty genius way to store all the relevant game files - levels, sprites, textures and everything else into a single file. This ensured that Doom is easily modifiable, which wasn't quite a commonplace feature at the time.
Carmack realised that many people had tried modding with Wolfenstein 3D, but the procedure was incredibly difficult, so he made it easier, in spite of significant friction from the more business-oriented members of id Software.
You can learn more about Sigil on Romero's website here, although if you're looking to buy any of the game's special editions, you're a bit too late. The megawad, however, launches for free, so go dig out your Doom.