I'll agree that the intentions for this season were very impressive. It's true, it seemed like everything was coming together for an epic finale. And, from far away, it seems like there's nothing that could be wrong with it. The characters develop in interesting and original ways, the BBEG is definitely different than anything we've seen before, and past characters are returning in new ways. I have two problems with this season, one much bigger than the other. The first and smaller problem is the lack of WR&H. I always thought that having them as a consistent enemy gave the show a lot of cohesion. Unlike Buffy, where very, very few story archs go through multiple seasons, Angel has a common goal throughout - beat Wolfram and Hart. Unfortunately, WR&H get slaughtered in the first half of the season, and disappear until the very last episode.
The bigger problem I have is that the episodes aren't that good. You can have great, original storylines, and AtS s5 does, but if you don't have good episodes to back them up, the result still won't be good. For me there are too many bad or meaningless episodes for this season to be good. Other than Orpheus and Soulless, I really don't like the middle of season 4.
So, in the end, I do agree with you. Joss tried to do something big, and, IMO, it didn't work.