I'm gonna say in the middle as the amount of hate she gets seems to be even with the amount of love. She's not completely neglected in polls but she's forgotten sometimes. She isn't as talked about as some of the characters but she isn't pushed to the back either (like a character such as Lucius).

I think as a character Bellatrix is awful, I hated her in the books, nothing good about her.
But because everyone loves Helena bonham Carter (I DO TOO! SHE IS INSANELY TALENTED) fans seem to adore Bellatrix because shes funny and bitchy but forget the fact she's not Helena, she is a mean old bitch!

Okay yeah but overrated and underrated doesn't have as much to do with liking or disliking as it does the amount of attention the character receives right. Right? You can like a character that's overrated and one that's underrated. And vice versa. Taking it in that route; Of course fans like her, that's what fans are. And when you really think about it, she's got a hand full of them (at least on fanpop) we're simply really vocal. There are less polls about her than (say) Hermione and Snape. I counted 2 specifically about her in the 7 pages I clicked through when looking for the links below. However she still gets attention so she isn't underrated either.

Factoring in like vs dislike she's still more middle ground. Of course she loses the first one it's Hermione.
I mean look at every poll she's ever been in. She pretty much always loses; link
But she was eliminated first or second in this contest; link
Due to this it's almost safe to say that she's one of the most hated characters in the series...I mean the results show themselves. However as you mentioned she still has her fans. So I still say middle rather than underrated.

Furthermore--I definitly agree some people only like her because of the beautiful and talented Helena. But for me personally, I started liking Helena after seeing her play Bella. Up to that point I didn't even know who she was.

Even further overrated means that the character doesn't deserve the love he/she gets. Tbh I think Bella deserves that hand full she has. She's a very interesting character. She's really funny and pretty badass to keep it simple.
Of course whether he/she deserves the fans or not is also subjective.

I'm not going to go off on you or argue with you (so if you don't want to debate about this do speak up). Hate who you will and feel free to vocalize it. But I really would appreciate it if you didn't call her a bitch. That's just kind of...unkind? to the fans she does have.

I don't personally care for her as a character, and many feel the same way, but there seems to be a group of fans that adore the heck out of her.

there seems to be a group of fans that adore the heck out of her

Hi. :D

^^^ You were definitely in mind! Lol.

ಠ⌣ಠ

I think she's really cool in the movies (what Nicolas97 said!) and interesting in the books, especially her relationship with Voldemort, but I think the hype around her is exaggerated (and what meow_lps said just proves that).

.coughs.bbp.coughs.

I think the amount of love she receives is pretty much equal to the amount of hate.