Extraplanar frat bros: just what D&D needed!
Jokes aside, bacchae are pretty good! They got a nice chassis with two outsider HD, modest boosts to all stats except intelligence (+0) and wisdom (-2), some neat defensive traits in acid and electricity resistance, polymorph immunity, and SR 11, and two natural claw attacks.
Furthermore, bacchae get 2/day Rage, which is actually more than most barbarians have by then. They also get Rake, but that's not too relevant as it forces you to use both claws.
On top of that, they have some SLAs. 3/day Charm Person and Hideous Laughter are hardly bad at low levels (though the latter will be penalized against non-outsiders), and 1/day Emotion is bigger magic than nearly any PC has by now. I'm not sure how updating works when a spell gets split in three or four others that all have different names, so I'll just assume this SLA is the original unedited 3.0 version (in which case it's a very versatile buff/debuff/utility/SoL spell).
Finally, as an ability that I'm not sure will ever come up in gameplay, bacchae can attempt to ensnare and permanently transform those who join their carousing. Technically, it should be usable as a sole character, but the DC of 10 (which the target must fail twice) is going to limit its usefulness. Then again, convincing the BBEG to go out for drinks and turning him into a drunken reveler sure nets you some style points.
All things considered, I'm comfortable with assigning bacchae +1 LA. A direct comparison is tricky, but barbarian is probably closest, in which case they have more rages, better stats, and some good SLAs backing it all up. Also elemental resistances are nice.