I also work at a math magnet and use Investigations. Our school also is on a math grant for a program called Direct Mathematical Thinking (DMT). It teaches kids strategies other than the traditional algorithm, like they do in Japan, China and the Netherlands which are always the top 3 countries in mathematics. Learning something new and different is always hard, but after a year of teaching with Investigations (and DMT) and seeing how it really gets the kids a deeper understanding of math concepts, I am sold on it. I understand people's reluctance, but our nation is very LOW in math standings so the traditional way isn't working.
Kids do learn their math facts, BUT not through rote memorization. Of course their are holes in Investigations, but there are usually holes in all math programs. I think that's the fun part of being a teacher is being able to fill in those holes. No curriculum is truly complete.
I recommend a book by Van De Walle that has great math lessons in it that really take things to a deeper level. I got it on amazon for under $20 and I refer to if often for math activity ideas.
If you want to talk further PM me. I know the frustration with Investigations, but my suggestion is just give it a chance! I also know the pressure of working at a math magnet, so if you want to compare notes...let me know!