I first experimented with phpBB sometime in the 2.0.x phase. I thought the installation process was helpful, and painless. The main shortcomings that bothered me in 2.x have been flexibility in setting up and applying permissions. However, in phpBB3, it seems as if improvement jumped light years ahead. I can honestly say it's on par, if not exceeding, in many areas, paid software like vB or IPB.
Another thing I thought was amazing was the update process from Beta4 to Beta5! It was awesome how I could maintain modified code, and view changed files side by side with the current versions. A truly superb job, I'm sure phpBB hackers (?:will|are) lov(?:e|ing) it. Note that when I say hackers, I don't mean crackers (nor script kiddies).
Being a PHP programmer myself, seeing the new module system is amazing, and it should make installing certain MODs easier than ever. if phpBB gets any more modular, the need for MODs like EasyMOD may cease to exist. Also, the releasing and application of patches will be much easier. I've enjoyed exploring the source code, and I've already changed several things here and there to get more familiar.
The depth in the CPs (especially the ACP) and the rest of the board seems as if we went from 2.x to 4.x. The phpBB development team has really outdone itself! 8)
Curtis
"Do, or do not. There is no try."
Yoda