I thought Rupert did a great job playing a thankless role, and I rather liked Myers - remember Myers was brought in to help Hellboy 'become a man,' not to be his babysitter - that's what the 'Nanny Squad' was for, and they failed miserably anyway as they tried to keep him out of the public eye. Broom was dying, and he knew Hellboy would need someone to help him deal with being without the only family he really had. Much as Abe is like a brother to him, HB's 'don't give a damn' attitude isn't for Abe - he is rather insular and bookish, and being an aquatic blue fish-like being doesn't help either! Hellboy needed someone human to rely upon.
However, Myers' non-inclusion in the sequel was determined long ago, since before the first film was even made, as the sequels were already well-outlined and plotted out by Mignola and Guillermo. I'm hoping there will be a small cameo for him, as I thought the character was fun. Oh, and his inclusion in the first film was so that audiences could associate with him as he was introduced to the weird and wonderful world of Hellboy, Abe and the B.P.R.D. Not everyone knew who Hellboy was before the film came out! Guillermo determined years ago that the Hellboy sequels would embrace more of the Mignola arc and plunge deeper into the world of folklore and myths, which is fine by me.
HM