I gave this some more thought, and honestly I'm just still really disappointed with these guys. I figured I'd vent in one last post (before going back to my ME 2 playthrough, ironically enough).
Those who are saying a Prothean is not important aren't fooling anyone, and I find it hard to beleive they are even fooling themselves. The fact that there is a living Prothean: that alone is massive enough to warrant being in the game. Protheans have been a massive part of the lore and backstory of the Mass Effect universe and of each of the games; for them to write this off as minor enough to be a small DLC is rediculous.
Now of course you could play through the game with the Prothean. Just like you could have Mass Effect 1 without Wrex, Star Wars without Darth Vader, Batman without Joker, Watchmen without Rorschach, and King Henry IV without Falstaff. You could remove a lot of fluff from a lot of games, movies, and books. That doesn't mean you should. Having a Prothean as DLC just hugely undermines the significance of the species built up in the past two games.
Now I really find it hard to believe that they thought of throwing in a Prothean at the last minute and decided to use it as DLC as opposed to altering the finished product, but regardless that shouldn't matter. Pack it with the new copies of the game. I mean really, did they write the story and then think to themselves "oh I know, let's have a Prothean as a downloadable character!" Did they really think a living Prothean could be written in such a way that it could be taken to be as insignificant enough to warrant its position as a DLC character? Please. Nobody complained about Kasumi, nobody complained about Zaeed. They weren't that special. They weren't that important. They were fun to have but you were not missing a large chunk of the story and lore without them. Yes, I realize that you can complete the story without the Prothean: this does not make him insignificant. The fact that he's a living member of a thought-to-be extinct race in significant enough. And if he isn't significant enough to warrant a position on the main game, then I really have to question the competency of Bioware's ME 3 writing staff.
That said I doubt I'll cancel my CE preorder. Partially because I still want to see the series to the end... and partially because I paid for it over BestBuy online with a pre-paid credit card and I'm not even sure if I could get my money back now without a huge hassle. But if this is what it has come to, I'll be sure that ME 3 will be the last Bioware product I buy.