ANGEL RULES!
Hey, definetely give Angel a chance. I did after watching Buffy and it is friggin GREAT! The 2 greatest shows ever created. So far Angel has equaled Buffy IMO. I didn't think that was possible after watching Buffy, but they are so close in quality it's scary. Angel's seasons are a bit darker than Buffy, but the seasons are fantastic.
If you watch I really recommend you only do it by watching from the beginning of season 1. It'll be the only way you will ever like Angel as much as you could. You have to follow the stories, get to know all the characters, otherwise you won't care at all about the characters.
I say get season 1 on DVD off Ebay or something. If you don't have much money than just sell it after you're done to get season 2.....and so on (or just get netflix and rent all the discs in order).
All the seasons of Angel are good, but when season 3 came around I was COMPLETELY hooked on the show. Angel Seasons 3 & 4 are incredible. So far 5 looks to be great too. If you watch it, it's a must to watch from the beginning. The characters are fantastic and evolve from beginning to now, so if you watch I really would suggest not jumping into season 5 first.
PS: You asked if there is anything you need to know about Angel. The answer is "YES!". There is a TON. Every season is much different. The locations have changed, characters evolve, characters have come and gone, died, etc. You really should watch from the beginning if you want to give Angel a fair shake. IMO, Buffy & Angel aren't the types of shows that should be jumped into at anytime. They should be watched from beginning to end.