If ME3 is bad, there's little I can do but bag the crap out of it every time it ever comes up.
I didn't like ME2 as much as the original, it detracted as an RPG, and the shooter elements were also diminished from my perspective. I think EA has (hopefully) pulled its finger out, and will alter ME3 to return to the roots of the original, it may do so, it may not, speculation is just that, but at any rate, once we've bought the game (especially PC versions in Australia), we're virtually stuck with it.
To be honest, regarding how I predict I'll react, there's only two reactions, there's "Oh my god, this is way beyond all expectations" and then there's "Well, what a shame, this could've been spectacular." There's a very thin line inbetween I feel, which I don't think it will fall on.
Given EA's recent performances, I must say my expectations are certainly lower now than they were previously, now I just hope they release it on time, the story concludes well, and the combat isn't as bad as ME2's, anything beyond that and I think I'll be satisfied.