Genesis 6:2 says that they found the human women beautiful. One may interpret that as they wish, especially in light of a better understanding of sex and genetics. But I think it's a stretch to assume it was anything else, because there isn't anything in the text that we can extrapolate from.
Genesis 6:1-8 reads like a bit of a mash-up of two (or perhaps three) different stories or story threads. God's disillusionment with mankind is one of those threads, the 'sons of God' are a different thread. Taken in isolation, verses 2 and 4 tell a tale of how angels married human women and fathered sons who "were the heroes of old, men of renown." They do not sound like villains, nor does the text imply that they were the cause of God's consternation with mankind. The verses seem to be out of place.