it's pretty good so far. pretty hard too, on well done. you can tell it's a build engine game because throwing dynamite at stuff is far more effective than any other method of attack, at least in the first act. hopefully there will be more napalm in the future as well - it was pretty limited so far.
but one of the things i've come across is that it's way harder to find out how things work in blood, and many other retro FPS games where the source is out there, than it is in doom. compare these two wiki pages:
the doom wiki tells you how this stuff works down to a tenth of a degree. the blood wiki doesn't even tell you how much damage it does, and i can't find a good source of this for this or other build games either. the quake wiki, for what it's worth, does have damage information. the blood wiki also does have enemy health, which is nice, but not particularly useful without knowing how much damage anything actually does.
presumably at least part of this is the prevalence of doom WADs as a delivery format for custom campaigns. but there are plenty of those for build and quake engine games as well. i guess this is all leading towards trying to convince myself to start reading source code for these games. not that i need this information, or that i am going to start duct taping a protractor to my monitor for optimal shotgun usage, but it would be nice for that stuff to get out there. maybe it's buried in a forum or something somewhere, but that isn't great either.