There's always this myth of "oh, well if you just go work for this tiny boutique firm, you can work on interesting things AND still go home at 5PM every day!" I've never actually met anyone for which this was true.
Sure, there are firms where you can go home at 5. They are usually paying you 60% of market rate to do work that could just as easily be outsourced to India. Very low-value stuff. Either that, or they have some niche market sewn up (i.e. they do some type of finance/law/consulting that no one else does, or they have connections that no one else does, etc). These are very, very few and far between.
As for the partnership part, most places are up-or-out, whether they explicitly say it or not. No one wants long-term middle managers hanging around. So it's generally partner track or go do something else. The whole business model is built around this.
I'm speaking mostly for finance, consulting, and accounting here. It could be a bit different in law given the breadth of different types of law, though at least in BigLaw, I'm sure it's not.
I probably won't stay in forever, specifically because I don't like the hours and pressure. But I recognize it for what it is.