I liked the Elves showing up -- it was dramatic and cinematic and made the early battle more interesting.
FWIW, I think there is a bit of book snobbery going on here. Books and movies are different -- what works in one doesn't necessarily work in the other. The fact that the films were made at all, and so well, is a testament to not only unbelievably long odds, but unspeakably hard work by the filmmakers on every level. It is possible to value both the books and movie separately for what they are without denigrating one to lift up the other.
Originally Posted by Nathanael
like Legolas, he and his comrades from Lothlorien were most likely Silvan elves who never made the journey to the Undying Lands)
Although he counts himself as a Silvan elf, Legolas is of Sindarin descent, at least on his father's side. Thranduil and Oropher come from Doriath in Beleriand, and crossed the Misty Mountains to settle with the Silvan elves already there. They didn't like the Noldor at all and wanted to blend in with the Silvan elves. (See LotR, appendix B, and Unfinished Tales, appendix B.)