Made it to level 10 in HR, then stopped to deal with my IM’s. After that, I took to reading the Doom Wiki to re-learn about the power ups (manily the spheres). Then I found out… the plasma gun and shotgun were based on toys.
And guess what? I owned both as a kid :
http://content.kapowwe.com/images5/1-1-465_13.jpg
http://web.archive.org/web/20041031174054/http://www.strombecker.ca/products/viewproduct.asp?ID=317