I played this game back in the day, and it has some of the typical old-school fps characteristics: The levels are seperated by a switch, followed by statistics, and has an individual name and position in the campaign. When you die you don't get reset to a checkpoint, you get back at the beginning of the map with the same weaponry at the start of the campaign. In this game its just a pitchfork. The AI from the enemies is not very sophisticated, the enemys attack that thing which did damage to them (the same AI like trash mobs in modern MMORPGs have), which results in battle royals with big groups of enemies.
But hey, it is just what you expect from an old-school fps, and this doesn't make the game any bad. You get used to the disadvantages it has, and it is the most modern old-school fps imho, an argument which is tied to some fascinating facts.
The end of the level has a little preview of the next level, like a sight through a fence, on a haunted house which will be displayed in the following map. The switch to end the level is just ornament, and not even mandatory at the end of every level.
The level-design from this game is just genius. It uses many detail to picture realistic levels, which remind of places everyone has seen or can picture, far better than Duke Nukem 3D for example. It has the best train level I have ever seen in a game (followed by the one in Goldeneye), the ghosttown map, which is a little town, but with cool architecture, or a ship stuck in ice
The wapons are very creative too, I still wait for another game to just hand me a gascan and a lighter to improvise a flamethrower. It has the first Tesla Cannon I know of, instead of a rocket luncher a napalm luncher (the enemies are f****d), an sawed of double barreled shotgun which you can decide to shoot the bullets single or simultaneously, TNT which can be thrown to detonate on impact or with a fuse, or with a proximity sensor, or remote triggered. And it has a voodoo doll. I mean, WTF!!!
I too love the enemies, crazy priests with machineguns, zombies which can be only killed by burning, decapitation or massive damage, hands without a body who try to choke you (aka homunculus), gargoyles which are statues one moment, before changing in winged beasts of doom. Spiders which make you drowsy, other spiders which make you poisened, fishes which can walk on land, and hellhounds which attack with fire, and send you burning.
I have played most great, good and mediocre fps games out there, and every new one of them, I compare to some of the best fps i have played. and Blood is the only one of the old-school fps I compare it to, because it is just great, with intelligent levels, fearsome enemies and great weaponry.
The downside is the limited engine, which can not be played in a window fluidly. Also the game looks kinda strange in abnormal degrees (for that time...) which you get using mouselook (in these days only a few weirdos used mouse in fps). The enemies are just bitmaps, but well crafted ones, not that iffy like the enemies in Duke 3D. And, last but not least, the game is very hard on higher difficulties, I don't think it is possible to finish it on the highest one, though I would like to be proven wrong.
So, it is a lesson in shooter history to play this game todays, if you have never played it. It is also one of the first games from Monolith Entertainment, and you will see some elements which even today is used in some of their recent games, like the F.E.A.R. - series. If you can stand its sheer old-schoolness, you will be greatly entertained.