Yes.
I like it a lot. Especially Irresistible Command. Also that the mace sets you on fire.
I'm a little worried that it's Auras are enormous (out to 5 squares away from it?), and 15 damage/round to all melees seems, er, excessive, but who knows how many HP characters have, and/or how easy it is for epic characters to negate that (I'm guessing it's a lot less easy than 3E).
Not giving the PCs XP for the summoned devils seems wierd unless they factor that into the XP for the Pit Fiend itself (if they do, then yeah, that's a simplification and good - otherwise it seems a tad stingy and MMORPG-esque). I wonder why it has to spend an Action Point to use Infernal Summons? To make it uninterruptible/instant or something? Recharge "4 5 6" looks interesting.
I like the tactics discussion, and the fluff is solid.