I'm definitely in the pro-Angell group.
That's not to say there are no negatives to the character, but I still think she's worth keeping around.
Kelly Hu left NY, so I personally don't see the appeal of wishing she'd come back--it's just not likely. Sure, she was a fun character, but I think Angell is a fun character too.
I'd like to know more about her, like why she's a cop. I'd also like to see more of her being the young, inexperienced detective--her scenes with Mac in "Not What it Looks Like" immediately come to mind.
As for her taking screentime from anybody--the only person who I can actually believe she'd take time from would be Flack, and even that I don't really see. I certainly don't think she takes time from Hawkes, considering that they have completely different jobs and all that. Plus, Angell has been in, what, six episodes this season? That's only like a third of the episodes thus far, so she's not there
every week. If the detectives don't get a lot of screentime because of the science in that particular episode, then it doesn't matter if she's there or not. Most of the time, Flack seems to be on the main case, and he's still the main detective. Plus, he can't always be on both cases, so there
needs to be a second detective around. Maka was fantastic during seasons 1 and 2, and Angell is doing a great job so far in season 3.
So, that's my two cents on why Angell should stick around.