Angel is angry that Spike got a soul and only angsted for a week while he has been suffering for over a century. This is because of how they got their souls. Spike went and had his soul magically implanted back into him. Angel was cursed with his soul so that he would forever be tormented by all he had done. It is virtually impossible for Angel to ever truly process and move on because the curse locks him into feeling like he can never atone for his crimes.
If you just watch Buffy you have to how the world has lasted this long, given that The End of the World as We Know It always seems imminent...then you watch Angel, and find out that Wolfram and Heart are behind almost every evil thing on either show, and THEY DON'T WANT TO WIN, meaning that all of Buffy's enemies are being played for suckers.
Illyria wonders at the Wolf, Ram and Hart being such a powerful entity when in her time they were little more than a joke, this is explained enough by the absence of Old Ones on earth that lowers the bar considerably, but it could also come from the fact than the senior partners thrive on the evil in every human. Since humans now dominate Earth, this would give the senior partners that much more power.
Angel's evil and soulless alter ego is called Angelus, the series is set in the city of Los Angeles. All of them different translations of Angel. But given the film noir set up of the show, Angel knows that as long as he remains in that city, helping the helpless, his dark side will always be there, and all around him (as there are always people around, and he is still a vampire, and even with a soul he still has to fight his bloodlust daily). And as Wolfram and Hart reminded him, evil will always exist there.