Barely playable. You're given bare armaments, and have to contend with using a shotgun against Hellknights and Revenants until you drop down a hole, get stuck in a maze of tunnels filled with enemies, and then find yourself in an outdoor area, still unarmed, but surrounded by enemies. Honestly, I think Sisyphus has it easier.
this is the kind of wad that if you got a group of newb players who want to get into custom levels, this is a fun start. it starts out easy, managing to stay easy for a very long amount of time until the halfway point. most areas are rather open, making maneuverability a lot of fun. the endgame levels are quite varied, but the overall enjoyment from playing GMP remains strong. a few unique ones here and there, like the Evilution tributes, MAP30, and MAP32, all worth it in the end.
Not a bad WAD for 1994, the time the level was created. For such a unholy temple, it isn't very bad to plow through, and a little dull in some rooms, although some add some weird designs to stand out. The lighting is nice and the map isn't too confusing nor frustrating. The WAD might be good for a casual level to plow through, so it may be worth a shot if you are into some old obscure maps.
The idea of the map isn't really, bad the execution is rather sloppy and while being nonlinear isn't something I see as a bad thing, there is really nothing stopping you from beating the map in 15 seconds or less if you somehow found the exit first try. Textures are sloppy, most rooms are cramped and tight to enter, buildings are thrown in randomly yet the rest of the outside map is just empty apart of a few trees. Monsters teleport inside the buildings or outside them every now and then, and it is nice that they teleport to "random" areas of the map instead of 1-2 fixated ones. However, there just isn't much here, it's pretty much what you can expect out of an old WAD.