Shredder's playing style is more positional than tactical and it plays with positional threats and can squeeze the most out of a position.Supposedly when practicing against Shredder at lower settings it simulates a human player at any playing strength by making typical human mistakes. It also has a variety of pieces and boards both in 2D and 3D, a built in coach, direct access to huge online endgame and game databases, etc, etc…all the things we have come to expect in any program.
Of course any engine will beat you up pretty bad tactically, but if you want to evaluate a game from the positional aspect, some of them give quite different evaluations. I’ve heard Komodo is well ahead of most engines when it comes to positional evaluations but personally I’ve found my free version to be unreliable.
If you are playing against other engines or engine-assisted games against other players then Houdini, Rybka or one of my favourites, Deep Saros, are the engines of choice. On the CCRL rating list Deep Shredder is ranked tenth behind such staples as Houdini, Stockfish, Rybka and Critter, etc.
On the other hand if you are using an engine to analyze your games with the idea of improving your play, then Shredder is an excellent choice.
I should add that when some time back I had a minor problem with Shredder I e-mailed for help and received a reply the next day, so their service is excellent.