Pretty much; way too powerful. Hopefully in Skyrim they find a way to temper that, by making it consume way more mana or making creatures that can still detect you or something. The fact that you can fully replenish mana before your invisibility wears off makes you next to invincible; at that point it basically becomes a matter of what battles you choose to fight. I try to use it as little as possible now, but ignoring it is like having the RCP-90 in Goldeneye and not blastin' fools with it.
I'll have to try out that Acrobatics trick, if for no other reason than something else to do in that game until I pick up Skyrim.