Our server tried B4 and we were generally pretty positive on this map. A common complaint was the dearth of health packs specifically. The layout feels a little maze-like at times, since two doors next to each other will often lead to radically different places. This isn't necessarily a negative, since it meant RED couldn't ever cover every BLU route for free, and BLU didn't become overly biased towards one route or the other by the map design.
I'm generally a big fan of sneaky vertical hidey spots, but there were a couple of roofs like the one in this image that felt kind of bad as BLU when RED took advantage of them.
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