Honestly, I've read the spoilers in their entirety, and I find the people decrying the plot as ridiculous and hackneyed to be acting in a patently absurd manner. Bearing in mind that this is just a script with a rough outline full of writer's notes and shorthand terms for certain things, lacking any of the presentation that makes a videogame what it is, these people would probably have groaned about how Vader being Luke's father was moronic if they read an early draft of The Empire Strikes Back.
Based upon what I've seen, the story will be very good and will make for a stunning, striking game that will undoubtedly be remembered as the best of the series and one of the greatest in BioWare's history. The only BioWare story I'd consider better would be Knights of the Old Republic's; whether the game as a whole is better than BioWare's hallmark, BG2, will be debatable, but the story itself is certainly one of the most solid they've ever put out. If you were expecting a Donnie Darko style head-trip from it, then you were always going to be disappointed; the "twists" and "surprises" in the previous two games were hardly anything that would make your head spin, and you were deluding yourself if you believed ME3 would be any different. What it will be, however, is an emotionally-charged story that serves as both an epic conclusion to Shepard's own struggle and offers fitting, powerful resolutions to the squadmates who have been developed over the course of the first two games. ME3 won't wrap your head up in knots, but I don't think anyone truly ever thought it would -- what it will do is tug deeply on your heartstrings and leave you very satisfied with the journey Shepard and his friends have been on since ME1.
Yes, there are certain parts in the script that are somewhat cringe-worthy; there are always going to be sections of any story that you find lacking or think could be done better. There are also some interesting parallels to other notable science-fiction works, particularly Babylon 5, which does make me curious as to how many of the writing/production stuff are fans of B5. In the end, though, like B5's own ending, I think ME3 will be a unique, powerful, touching experience that, while it might end exactly as it was foreshadowed and exactly as you expected, will nonetheless leave you at a loss for words when the final credits roll.
On a final note, for those who are claiming that your choices from the first two games will have no impact on the story whatsoever, this is patently untrue. The basic core of the experience will remain the same regardless of your choices from the first two games, but again, this was always going to be the case; if you believed that the choices you had access to in ME1 and ME2 were going to drastically alter the story structure, then you were deceiving yourself. What will be altered is the experience itself, and I remain confident from what I've read in the script that experiencing the story through the lens of different choices will alter the way you view the story significantly. Basically, the structure and flow of the story will be the same no matter what you've done -- as it was in ME2 -- but the way the story unfolds will be vastly different depending upon the choices you made, and the outcomes and endings you have available will likewise be altered based upon your decisions from the previous two games.
Oh, and Jacob!