This map has a fairly typical hub-style layout, you begin off one branch, play through some linear rooms leading to a crossroad of sorts, then proceed to find each keycard to open the appropriate doors. The game-play ramps up appropriately swiftly for a single map, and it was only a few minutes running through some imp-infested white corridors before I was greeted by a hell knight in an office!
The main hook of this map isn't just the layout, but the visual style Sergeant goes for: A foyer, filing rooms, office cubicles (this is the area you'll have to cross through a few times - the cubicle walls make for some useful cover), a dimly lit storage room make for a refreshing change from the usual military base designs. It didn't take me very long to finish, perhaps half an hour at most - and I play every map on Ultra Violence with fast monsters - but it was a memorable little journey with a perfect challenge level, a couple of cool traps, and some unpredictable monster placement. For a "speedmap" this is worth your time.
Ah, some ZDoom features! I find it makes a pleasant change to play the odd map with slopes, swimmable water and the like. Bloodriver Outpost makes good use of both: this is probably the first occasion I've had to crouch under some slopes to pick up some items, in Doom!
A cramped base entrance opens almost immediately to an open area (shown in the image), though I was already given a super shotgun, I was assaulted on all sides from Cacos, imps, and a few hitscan enemies. A couple of quick runs to pick up some enemies, and peeping my head out of the nearby secret, was enough to get some infighting going amongst the monsters, and this eased things somewhat.
A few button presses and a quick swim later, I reached the other side of the open area, leading into more base rooms and enemies from various directions. The level design move to a more room-based Quake 2-style at this point, punctuated with one or two more outside areas, with varied monster choice and placement keeping things interesting. The only irksome point with this map is that it becomes a button-fest, doors, rooms, floors opening progressively as you kill enough enemies to hit the next button.
Even with the caveat this is strongly recommended, I enjoyed my time with this map and found the difficulty just right. I'm not against using (G)ZDoom features in Doom maps, and in the right hands they augment fun map design with elements that can bring out further diversity in the gameplay. Good job Henri, keep it up.