After leaving Windows, I found myself missing Xplorer² quite a bit (still do) and it doesn't quite work in Wine, so I've burned through plenty of file managers on Linux trying to find a reasonable facsimile. So far I have had to just grumpily sit down and use
Thunar. It gets the job done, I like the choice between traditional file path/breadcrumb path modes and the choice of tree view or XDG bookmarks in the left panel, the custom definable actions are very useful, AND...
it comes with my favorite desktop environment, Xfce.
Other file managers I've tried either don't work well, try to do too much with too many icons or are annoyingly minimal.
I purposely ignored Dolphin, Nautilus and Krusader, as I've never been enamored with either KDE or GNOME. I have my reasons.
Here's all the ones I remember trying, with all the beauty and warts I can remember.
Midnight Commander - If you have fond memories of Norton Commander and it's imitators, you'll like MC. First of all, dual folder panes rule. On Slackware, it doubles as the package manager, which is handy, and did I say dual folder panes rule? One of the first things I install if it's not already included, as it is an absolute necessity if my X goes down.
Xfe - Comes closest to being comparable to Xplorer², though still a little rough looking (uses the Fox Toolkit) and a lot of features up front that I never used, but it has what is most essential: a tree view and two file panes. That rules plus one. For some reason, the devs tacked on a bunch of desktop extras as if it was on it's way to being a new window manager. Did not want. Looks like they've scaled back recently, maybe I'll give it another shot.
Rox-filer - Too damn minimal. Sorry, I have nothing else to say.
DoubleCommander - Dual file panes rule, but this one didn't feel completely right out of the box. The font was too bold, and having directories in brackets I find superfluous and distracting, but most aspects of the GUI are easily changed from the preferences, and the rest of it is pretty solid. I would like a tree view to go with the dual panes and
XDG bookmarks instead of drive icons, but I digress. I've been trying to give this one more face-time to get used to what it can do, but haven't been successful at that. Developed with Lazarus/Freepascal
Emelfm2 - Dual panes rule (is there an echo in here?), but this one tries to do way too much with icons, IMO. Quite configurable, with lots of good features, but I gave it up after a month cause it just didn't
feel right.
Gentoo - Dual panes ru... SO MANY BUTTONS AT THE BOTTOM!
Worker - See Gentoo, above + Tk interface (or is that Motif?). Either way... Bleah.
SpaceFm - Dual panes ru... sooo many panes... my God, it's full of tabs... o_O. I know this one has been mentioned, but I gotta add my two cents and say the possibilities for 4 panes each with their own tree view is pretty darn impressive, but I got lost in it. Maybe one day I'll take a deep breath and try again. It's still installed, so that's saying something.
MuCommander - Dual panes... written in Java. :\ Sorry, not much to say about that one either.
So, that's about all I got, I don't think I'll be 100% happy with any one file manager until I find a one-to-one clone of Xplorer² for Linux. Until then, Thunar is pretty useful as it is, DoubleCommander is almost there, and maybe Xfe will one day hit the sweet spot.
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And a fine desktop environ it is too, even if it is no longer the petit bureau it once was. 
