We had a good, rather lengthy discussion of this topic some time back here in the Forum. It eventually stretched into several threads; here's a link to the longest one: http://www.finescale.com/FSM/CS/forums/638643/ShowPost.aspx
I suggest paying particular attention to the contributions from jwintjes, who clearly knows the subject more thoroughly than the other contributors (and has far stronger academic credentials in the field of ancient ships than I do). As his posts will clarify, he has a relatively high opinion of the Zvezda kits - relative, that is, to the competition. But the unfortunate bottom line seems to be that none of the plastic Greek or Roman ship kits - either those currently available, or those from earlier decades - really forms the basis for a serious scale model without extreme modification - such as splicing in a section of the hull from a second kit.
In terms of detail and overall quality, the best of the currently-available batch probably is the Academy "Roman Warship." It's a beautifully designed and executed kit, but it has some major problems in terms of historical accuracy (starting with the fact that half of its oars appear to be missing). It was originally issued by Imai, which used many of the same parts in an equally (if not more) spurious "Greek Warship."
Part of the blame for this state of affairs lies with the kit manufacturers, who don't seem to have done (or particularly cared about doing) their homework. It should be acknowledged, however, that some of the problems aren't entirely their fault. In the past 25 years or thereabouts (i.e., since the Aurora, Heller, and Imai/Academy kits were designed) scholars have done a great deal of research that's significantly altered their impressions of how ancient galleys looked and operated. The full-size reconstructed Greek trireme Olympias has made it clear that many of the traditional assumptions about galley warfare were just plain wrong.
I've made this observation before, but I'll make it again in the forlorn hope that some manufacturer will read it: give us a scale model, plastic, wood, resin, or otherwise, of the Olympias.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.