Barbs are kinda weird because for 90% of the game you're better off multiclassing , but those endgame tier single class abilities are pretty sweet.
Barb/Fighter is very good for tanking
He can do some fun things with certain weapons, AFAIR. But I'd not trade a Swashbuckler for one.
Tactical Barrage is really what the doctor ordered to turn on Carnage (as is Confident Aim). Even cancels Confusion on Berserker until you can find an item (or Fighter passive) to do it. I consider Caroc broken so don't use.
The pull ability on Fighter is fast with no recovery and Fighter provides the extra Engagement Barb needs. Anything tries to leave gets a Full Attack triggering more Carnage for everyone stuck nearby.
Fighter also nice with Pal to get those Auras wider.
Fighter / Barb indeed has merit. Not my favorite combination, but very solid.
Edit: Really nice with morningstars. The modal Body Blows lowers Fortitude by 25 (!), which is great for Barb Brute Force (and Knockdown and...). Larger number of crits generally ofsets the lowered damage from modals.
And is great for party CC, of course. Plus with Willbreaker you can also debuff Will by -15, make the enemies Shaken and Interrupt them.
Although Lord Darryn's Voulge bound to a Barb is pretty awesome too.
However Fighter / Paladin is just silly IMO. There's nothing in the game remotely calling for this kind of durability. Being an immovable object serves no purpose IMO.
A Fighter is effectively immortal once he gets Unbending anyway.