Diana G.
Yelp
I have seen Porcupine Tree play here twice. This is basically an old gutted theatre with a balcony. My experience at the Forum has a lot to do with the band. Both times, the show was completely sold out, and I was in the very front next to the stage, and had a great time! Of course, when you're that close to the stage, there is no way you can get to the bar and back for a beer, so I advise to have a couple beers beforehand. If you get thirsty during the show, they may pass around cups of water to the people in the front.
On my second visit, the band had requested no cameras or taking of photos (which seems to be a Porcupine Tree rule now). So, they were searching bags for cameras, and holding them at the door until the end of the show. There was no way I was doing that, so I just hid mine in an inside pocket and it worked out fine for me. During the show, some guy not far from me pulled out his camera and held it up trying to get a quick pic of the stage, and security was all over him - twice! I felt lucky that on my first visit to the Forum, the band did not make that request, so I was able to get some great concert photos!
Overall, this is a great venue - probably the best place I have ever seen a show. It is very easy to find (just steps away from the Underground) and there is a fabulous pub & sandwich shop right across the street. If you go, get there early to get a good spot in the queue. If you have a ticket you cannot use, you will probably be able to sell it to the ticket scalpers out front. Also, I advise going to the swag booth before the show starts, because you will not want to stop there afterwards. If it's a great band, you may also be able to get bootleg swag out front afterwards. I was surprised they had bootleg Porcupine Tree t-shirts! =:)