Simply put, BFD2 is the nearest thing to a realistic drum sound you're going to get. The only other thing I've heard that comes close is the Abbey Road drums for Kontakt, but that doesn't offer nearly as much flexibility and depth.
This realism is, of course, down to the sheer amount of multi sampling (and obviously the recording quality of it), so it's not for the small hard disk/memory computer. I would say 2GB RAM minimum, but 4GB if you really want a smooth ride when using other VSTs etc. It also takes about 60GB of disk space with full install (which you want to do. There's options for installing less sounds. Don't bother. You bought it because of the amount of samples).
The other thing to note is that when you move away from the presets and start trying to shape the sound to your own specific needs, it's a fairly long learning curve. The realism comes from drum choice, virtual mic/effects setup, and beat programming, not just the samples. In the wrong hands it can sound fairly horrible. It's a beast that needs to be tamed.
But once you get your head and ears round it, it's just amazing. I actually think £150 is fairly reasonable considering the work that's obviously gone into it.