I hate lynch-avoidance roles except in very limited circumstances (I actually think a huge game like Capo has a lot more latitude for limited use of such things, simply because its size gives more opportunity for second chances). I'm not a fan of detectives and to a lesser extent town trackers/activity detectives, either. I have many fewer issues with roleblockers, town watchers, and the like. My basic criteria there is:

-- if an oft-metagamed player has the capability of preventing early incriminating results being produced on them as mafia/third party without compromising their team, then all is well
-- if not ... not.

As an example, a mafia team of three is set up in a hierarchy with designated killer, roleblocker/backup killer, goon/backup roleblocker/third-chance killer. There is an activity tracker in the game for the town. What's the mafia team now to do, if the oft-metagamed player gets the #1 killer role? You can't not kill, so basically you're resigning yourself to losing one of your players right off the bat almost by default, and no matter how well you are all playing otherwise. Now imagine the same team re-imagined so any of the three mafia can do the kill on a given night; or with an untrackable team kill plus three minor powers. The problem evaporates, provided at least that the oft-metagamed player has access to a decent cover role to explain his minor-power activity once caught (or the powers are so minor that non-use is not crippling).

That brings me to the other big gripe I have in playing (and generally losing) mafia roles: lack of (good) cover for the mafia. Without a strong canon source it's not as important; without a very powerful town it's not as important -- but generally as games are played around here some effort needs to be made in that regard so it doesn't turn into "lynch everybody without a good name claim/lynch all the vanillas/everyone without a verifiable night power is mafia".