Floorplan

Flow: Every area in this map has at least one way in and another way out. No dead ends.

Weapons and ammo: the weapons are spreaded out accross the different areas. The stronger weapons are not clustered in one area for example. The same for health, armor and power up.

Some weapons and ammo are mismatched. The ammo for that weapon is in a different area. I'm not a professional player but it seems to be done on purpose to force the players to keep running.

The U damage power up, armor and thin pads are each on a different corner of the map. This prevents camping and forces the players to run.

The U damage is in a spot which requires hammer jump and self damage to get it. Its location is also quite vulnerable to being shoot from whoever is at the balcony behind. Now speaking about professional players, the U damage's location doesn't allow for lift jump or dodges to grab it. That's something to consider when making levels aimed at e-sports.

The armor is located in a quite open area, with one pillar to protect the player from behind. The thin pads are located under a ramp, which is quite protected but at the same time could be a trap because there is nowhere to run under the ramp.

I can't comment much about how many health items there should be, but the health placed right under the U damage are there because it's the spot for hammer jumps, which does self harm to the player.

The Shock and Flak are strong weapons. This map creates close encounters which greatly favours both weapons. The rocket is also strong. The distance between the Shock and its ammo is large, which I suspect is to balance it since this map greatly favours shock combos.

The Flak is very close to its ammo and this map greatly favours this weapon.

The Bio is the weakest weapon and it's plcaed in a dangerous spot. I would change the Bio's location.

The Minigun and Pulse are close to their own ammo and both are weapons very suited for close encounters.

The Ripper is good with closed spaces and was placed in a narrow area which seems to fit it. However, I don't understand why its ammo was placed next to the Bio, very far away.

The Sniper isn't so great in this map because it doesn't have much room for snipping. Having its ammo close to it seems a sensible decision.

The U damage being close to the Shock, but the shock's ammo being far away seems a way to balance it. With this power up being close to the Pulse, Minigun or Flak it'd be very very strong.

A: This particular corridor feels a great spot to place power ups or strong weapons because whoever goes in is cornered. Enemies can come from both corridor's ends.

B: Why this gap and no bridge? No idea but maybe it's to force the players to jump and the jumping sound can be heard by other players.

C: Why the grates? In this game I think it's purely aesthetics. But with the water below and 3D sounds I'd imagine that the sound could have a greater impact considering a more modern tech.

D, E, F: I wouldn't place a spawn point / player start in a position like that. The player suddenly spawns and can be attacked from both behind and front at the same time.

G: This spawn point is even worse. The player can be attacked from all sides.

H: I'd move this spawn point to under the ramp.

Audio

I once thought that adding more water would make this level prettier. I looked at the drains and thought that water could be added there. Much later on I discovered that by having the water cover a much larger area than the original map, I had, unintentionally, made the gameplay worse. The players could no longer associate the water splashes sounds with one specific corridor. The splashes were spread over a much larger area, making it harder to track the players. Note that I'm not talking about realistic sound waves propagation because even if this game had this feature, that won't remedy the mistake itself. 

The lift near the U damage makes noise when some player uses it. The water also has the function of alerting other players that somebody is there. I suspect that the heal vials placed under the Pulse Gun also has this function of alerting whoever is above that there is some player under it.

I suspect that there is a lift where the U damage is and not a ramp or stairs because the lift makes a sound when there is a player on it. If a map has two lifts, having different sounds for each may be a sensible decision if this type of information is important for the game in question.

The wind and water ambient sounds in this level are there to make the environment more interesting and pleasant.

Scale and proportion

My method was to take some screenshots and take some crude measures. Sometimes you don't even have to measure, just count the number of times a texture tiles because they are almost always 256 x 256. UE1 lacks a ruler, what I did was to use the brushbuilder as one.

In UE1 the standard corridor and doorway is 256 units wide. Less than that it's too narrow. More than that it's too wide. The same for height, 256 units is the standard that feels comfortable.

The default player size in UE5 seems to fit comfortably with a width of 4 meters. That's my base of conversion: 256 UE1 units = 4 m UE5.