My mistake, I thought this one was the first of the 2 BS. (I always mix them up) Well... one year after Doom, this game has no excuse. While it had a lots of aliens, most of them fought exactly the same way (with the exception of the elites that faked death and of the ice sphere, mostly), which killed the feeling of diversity. So, not so fun, even back then. (contrarely to the first opus).

Do you know the amount of resources and time needed to make source code modifications AND make new content for an entire game? That, added to the time it takes for the legal proceedings of licensing an engine from another company. The wolf3d engine took long to be available for licensing. Developers only were able to license and use it very late, about the time id software's NEXT engine and game were ready, that being Doom. By the time they had finished and were releasing their own games, Doom II was already out. So it's sort of unfair to complain on that end.