I would hazard a guess that closers are historically waaaaay more erratic than position players. For every Eck, there's at least one John Rocker.
Mark Davis comes to mind. He had an All Star season in 1988 and then followed that up with a Cy Young season in 1989 whilest pitching for San Diego. He parlayed that Cy Young season into a huge contract from the Kansas City Royals, who had high expectations of him to be a dominant closer for years to come. He flamed out the first season with the Royals and never lived up to his reputation as a dominant anything. Nice pitcher? Yeah, he was, but never dominant again like he was in San Diego in 1989.
But back to Lidge.
When things start to catch up to you, one of the things a good pitcher will do is to simplify things. Fastball goes to the hands on the inside, down at the knees on the outside, slider can show itself at the strikezone and tail away or even down (although that is rare thing to do, but I digress), slider even can back up and catch some hitters thinking too much. Said simplification is okay to do, in fact it works quite a bit of time, but it never really leads to being dominant again. Dominance is rare, but to do so you have to have that one signature pitch you can repeatly throw without fail and even if the hitter knows it's coming, they still can't square you up. Mariano Rivera = cutter. Trevor Hoffman = changeup. Goose Gossage = riser (four seamer). Eckersley = slider. Billy Wagner = grip it and rip it. All those guys will show you other pitches, but when they have to get you out and you also know it, they will go with what they trust the most and forgetaboutit! Lidge had such a pitch in the slider that broke down and away from right handers and down and in to leftys (hence why some lefty hitters had more success against him... that is the wheel house for some lefty hitters). But when the league caught up with Lidge, they laid off the slider and that lead to inconsistency in throwing the darn thing. Lidge tried to do too much to be dominant again with the same pitch. Hence why he overthrew the pitch and opened up a lot. It flattened the pitch out because he desperately wanted to keep throwing the pitch regardless as his signature pitch and for strikes.
Now, since he's simplified his approach to getting guys out, he's actually doing much better. He's pitching more actually, so that doesn't necessarily means dominance any more. It also doesn't mean suckitude either. It means time will tell what sort of reliever he'll be. Even Dave Smith could close successfully with just one pitch... a nasty 12to6 curveball that even though you knew it was coming and it was in the low 80s, it was hard to hit and you just couldn't afford to sit on a fastball with Smitty. Lidge may be that guy again, but expectations of a dominant closer are just too much to ask of anyone right now.
Enjoy watching him mature as a pitcher and figure some things out. Who knows, it may mean he reinvents himself as well and makes the hitter have to think about more than just laying off the slider and hitting the four seamer if he simplify and execute effectively.
