[3.P] Assess Opponent

[ImperatorK]

That's the name of the Sense Motive ability from Complete Adventurer, IIRC. Is it good? If not then what are the alternatives (including homebrew)?

[StreamOfTheSky]

I never used it, always thought it'd be cool with the Combat Intuition feat but not worth the action w/o the feat.  But IME it's pretty obvious when something is massively above or below your ECL via DM hints, so I never bothered with it.

As for a PF option, Halfling divine casters (so Oracle I guess; only divine caster that's cha-based...) can get some keepsake to add an option to some level 1 spell.  They're almost all terrible, but this one kind of does what you're looking for and is cool:

"Jagged Dice: This pair of ruined dice is often given to young halflings to commemorate tasks that involve coordinating a group in order to accomplish something that benefits the community as a whole. A halfling who uses it while casting deathwatch can, instead of learning about the injuries of nearby creatures, gain a rough understanding of their relative power. The GM should offer a ranking of creatures by their CR (without stating their actual CR) from most powerful to least."

[Twilightwyrm]

This is actually one of the better things, for me anyways, to come out of Complete Adventurer. I tend to utilize this part of the skill quite a bit, especially since many opponents will take no steps to hide how powerful they are from you unless they have a specific reason to do so. It is generally a not much an issue when fighting monsters, since simple knowledge checks tend to cover the basic versions, but in campaigns where you are, overwhelmingly, fighting humanoid opponents (which is pretty much every campaign I'm in), or often fighting home brew creatures, who quite possibly have class levels, it becomes invaluable to know about how much more powerful than you they are. (Especially if your DM is a fan of adding weird templates to things)