It might take a bit to figure out what "disable HTC sense" means, but give it some time. I came from blackberry world a month ago for the exact same (sero) reason you did
Since then, I've flashed a couple roms, settled on the Energy rom, and still keeping tweaking it on a regular basis to suit my needs. The stock software does suck in comparsion though, there's not enough options. Once you get comfortable with it, you'll be adding apps just like any other phone, tweaking the notifications to fit your needs (mighty's notification blinking light cab is helpful if you don't want to constantly have the blinking LED for every email), and disabling htc messaging for wm messageing just like the rest of us
The search function on this forum will pretty much answer all your questions. So, no, I'd say you didn't screw up. You can't touch the functionality of these phones for what we're paying on a monthly basis for service. Actually, I'm jealous, I've got two sero's at $70 a month. So for what you're paying, you're not allowed to complain