Honestly, I'm not such a fan of Adrian's solo work. ASAP is too mellow, while PRR is too agressive for my taste. The only record he did outside Maiden that I like is Welcome to the World. Not just because of the great vocalist (where is that guy now, anyway? He is Welsh, or something like that?) Also, there are some great guitar parts on that record I'd never heard before from H...
Anyway, no matter what I think about his solo work generally, I think his (and Bruce's also) departure from the band had to be made back in the day. Two of them managed to express themselves outside Maiden, so when they came back they brought some creativity which was obviously missing, judging by the Virtual XI and general feel (to me) that Steve "fell asleep" in the 70's and tried to revive that period through the band's music in the 90's.