I have been doing a lot of testing for the sliders, and I can say no. It's bad all the way around. You'll see them coming out in wrong package sets. Test the Ask Madden feature if you don't believe me. Use the A option and play several games. You'll end up with a Madden IQ somewhere between 400 and 520 (highest I have seen). This will not change regardless of what the slider settings are set to, or the game difficulty is set.
Based on what I have seen, the Ask Madden feature is using the same logic as the CPU play calling, so at any given point in time your not playing anything harder than a 400-520 coach. This is unfortunate, because it's fairly easy to get your Madden IQ to the 700's, just by calling the right package sets and making the right situational choices.
That's why I use Beginner Playcalling and let the CPU call the game, because at that point you are actually playing a fair game. It sucks because you don't get to employ your own strategy, but it's more challenging from a gameplay perspective. If you want a challenging game, give the
NFL Simulation Sliders a try and couple that with a challenge from
Make Madden 10 More Challenging.