I think with my latest playthrough of Mountainside, I've come to a bit of a crossroad with the map. On the one hand, I REALLY like the concept of the map!! It's a fun, interesting attempt at downhill Payload that I think is a great time!
...However, I think the map still has its issues. When we played rc2 of this map (which isn't released on TF2maps, sadly :/), we hard-held at B all three rounds we played. That is not something you normally see unless there is something wrong with the map, which I think is a fatal flaw. Players mentioned a lot how the downhill nature of the map, ironically, separated a lot of the BLU team and made it generally hard for them to push. This is quite strange, as the nature of downhill PL is that usually BLU always has an advantage over RED.
Overall, while I had some fun on the map, I cannot ignore these glaring issues with the map. I never got to see any gameplay on last, or even C for that matter, so I am giving it a 5/10 for now. If I end up playing this again and come to a different conclusion about the map, I'll try re-reviewing this.
