See, I prefer Season 4 of Angel to Season 5. Season 4 certainly had it's downsides, but the good of that season by far outweighs the bad.
Connor, for example. Yeah, I disliked Connor, but obviously not as much as other people. Even though his "reason for being born" was simply written in because of Charisma Carpenters' pregnancy, at least it was a reason. That's what bugged me about Season 3 of Angel. They never gave a reason for how Connor was even born. It might be a dumb reason, but it worked for me given the circumstances.
As for Cordy being the bad guy, I had read somewhere, many years ago, that Cordy was always suppose to be the big bad of Season 4. If I remember correctly, the end of the season was suppose to be Angel and Cordy in this huge fight. So, really, no matter what, Cordy wouldn't have been Cordy in Season 4. I don't have a problem with that. Now, yes. I missed the "real" Cordy in Season 4 (and 5), but this was something the Wheadonverse had tried before and failed at (having one of the main, GOOD characters go bad). They tried it with Willow, and it just didn't work. At least with Cordy, they worked an entire season of her being bad and pulling the gang's threads. It worked. And at least we got "You're Welcome" in S5 to bring the real Cordy back.
Unlike everyone else, I didn't have a problem with Jasmine. I think it was meant to be a stark juxtaposition to the rest of the season. The Fang Gang was expecting the ultimate evil, and instead, the got someone who was bring around world peace. Yeah, it was at a terrible cost, but it was still world peace.
Season 5 of Angel suffered for a couple of reasons. Number one was Spike. I was a huge fan of his until he, uh, fell in love with Buffy. After that I couldn't stand him. Plus, they destroyed the wonderful relationship Angel had built with Cordy by having Angel suddenly back in love with Buffy. It made no sense.
Then there was the whole Lindsey arc that didn't make sense. And Illyria. And the Nazi submarine episode. Plus, Lorne, my favorite character, was reduced to the background.